After many years of camping trips, I decided to build a custom travel trailer! I’ve been working on this idea for a long time, and I’m excited to finally get started.
It has to be pitch black inside and very comfortable. I need my sleep and I like to stay up late. I really don’t want any windows at all. I always cover my bedroom windows with blackout fabric and sleep until noon.
It was also very important to me that it be fully off-grid. That means enough solar and batteries to heat or cool the space, cook food, and to make my own water.
I went for a very simple design which is highly utilitarian. I was inspired by designs like this and this.
I went for a simple rectangular shape using this 5×8 steel trailer as a foundation. There are 4×8 trailers which are a bit cheaper, but having an extra foot of width still leaves in narrower than my car while making a lot more space inside for activities.
I decided to use exterior sheathing plywood for the base and walls, with ground contact 2x6s for the framing. This makes the structure extremely strong and resilient. Finally I covered everything in white flex-seal which is basically a bed liner to prevent any leakage or gaps.
The rear wall of the trailer opens completely. It hinges up and onto a pair of gas pistons. This is great because it also acts as a canopy to shade the entrance, while allowing a great view of the outside world.
I purchased two folding memory foam pads which convert to either a bed or a couch. These rest on an elevated bed with about a foot of storage underneath and about two feet of floor between the bed and the door.
Above the head of the bed there is a 5,000 btu air conditioner and also a small electric heater.
I am including a microwave and coffee maker. These run easily off the lithium bank and allow hot food to be quickly prepared even in the most remote locations.
In the trunk of the car, there is a pop-up tent and a portable toilet. This comes in handy when you’re a long way from restrooms and don’t feel like digging a hole. Storing it in the trunk means there is no smell in the sleeping space.
I had planned out a complex system for filtering water and then using propane to have hot showers outside the trailer. I decided not to do this for several reasons. First, after a recent summer camping trip of several weeks in Tahoe, I learned that it’s easy to find a place to take a shower. Second, I can easily use a cheap pump sprayer to take showers just like we do at Burning Man. Third, I really don’t want to have any propane at all in the design.
It was very important to me to keep everything electric so that it is completely sustainable and can run indefinitely off of the solar panels. I really don’t want to rely on propane, partly because it’s a fossil fuel and partly because it is inherently limited and means I will need to keep refilling it.
My main source of power is the solar array. As a backup and depending on the weather wherever I happen to be, there is also a 2kw generator on the tongue of the trailer. Hopefully I will not need to use this
I think this will be plenty of power, but I am considering adding a second solar array to the passenger side of the trailer which can also lift automatically into position. This would double my available power for just a few hundred dollars.
Assemble The Trailer
So first let me say I am glad I bought this trailer and I would buy it again. The price is great and the 5×8 profile is great. But assembling it was a nightmare. The directions that come with it are completely wrong (apparently they are for some previous version of the trailer). It’s not too hard to figure it out though. It took me about four hours working alone to get get it completely assembled with the extras I added.
I definitely recommend running a separate ground line to all the lights instead of trying to use a painted frame alone to carry the ground. Also the market lights come with these stupid vampire taps. Just splice the wires properly.
I added several things to the trailer. First this wheel jack on the tongue.
Next, this security kit. It comes with a ball lock, a trigger lock, and a receiver lock for under thirty bucks. Great value.
This trailer has a 17″ hitch height (from the ground). My car is a 2013 Honda Civic LX which has a 12 inch hitch height, so I got a 5 inch hitch lift which is sized correctly for my U-Haul receiver (1.25″), and also the appropriate ball to connect the hitch lift to the trailer.
U-Haul charged about $300 for parts, labor, and wiring to install the receiver.
All of this is rated much higher than what I need for this project. You could probably cut some corners but I like to be sure that nothing will go wrong.
The first step in constructing the bed was to pick up four sheets of pressure treated 3/4″ 4’x8′ plywood. These were very expensive and probably a lot more than is really needed but again I want to make sure this thing lasts forever.
In this photo, you can see two layers of plywood stacked on top of each other…
Since the trailer is 5×8 but wood only comes in 4×8, it takes four pieces. The bottom layer is two pieces of 4×5 which covers the entire trailer but leaves a seam in the middle. So I decided to do a second layer which you can see above. This moves the seams away from the middle, eliminating any leakage or openings in the floor.
Here you can see the top layer is removed, showing the first layer only. Because the bolts that hold the frame together stick out above the frame, I decided to use a hole saw to cut holes in the bottom layer to allow it to sit flush on the frame. You can also see the big seam in the middle which would potentially let air and creatures in.
Here you can see a close-up of the 1″ holes which fit the bolts perfectly. You can also see a closeup of the seam which needs covering up.
In between the two layers, I put an entire bottle of Gorilla Glue, making sure to completely surround all the holes and the seam, so that once the wood is glued together, no moisture can get in between the layers.
Again this is overkill because pressure treated plywood is already waterproof but just to be safe I decided to go for the gold here.
Next I put the top layer back on, gluing it in place. You may notice I made sure to put the nice finished side down and leave the ugly side up. This was not on purpose. 😀
Next I put dozens of screws in to hold the boards together and let the glue set very tightly. I made sure to surround every seam and hole with several screws just to be sure it will be a good tight fit and last forever.
Last, I piled everything heavy I could find on top to compress the boards for the next 24 hours until the glue has set.
Frame and Walls
I decided to go with a simple geometric rectangle. I used exterior pine sheathing for the bed, walls, and roof with 2×6 deck boards for framing. Then I covered everything in flex seal which is basically bed liner. This is definitely overkill but I want to be sure I don’t have anything to worry about.
The rear wall swings up to serve as the door, and is supported by a pair of gas pistons. I used Autocad to figure out where to mount them based on the open and closed lengths to get the angle I wanted when the door is open.
I used pressure treated fir 2×6 deck boards with three inch deck screws for the framing, and then I also added steel brackets to every joint, and the same 3/4″ pressure treated plywood on the outside.
The framing is a little wonky because of the way I’m doing the mattress. In this photo you can see there is a frame around the front, and then on the front face where the front wall will go. I’m planning to add an air conditioner to the front wall, so there will be another cross member on the front.
There is also a frame around the midpoint so that the roof panels can be mounted at the seam. Then there is a third frame to support the end of the mattress platform. You can see the three cross-beams which are also mounted with both three-inch deck screws and steel brackets.
I am planning to add sheets of styrofoam to the voids between the studs and then cover the inside walls with nicer-looking plywood.
Note that there is another sheet of plywood in the bottom just for storage. It will become the back wall/door. Also that random board laying across the beams is just hanging out, not permanently placed there.
Making the front wall was a little complicated because I had a lot of extra wood and I didn’t want to buy another $60 sheet of this plywood so I did the same thing as the base and cut and glued several 3/4 sheets together to form a 1.5″ thick front wall. This is on the ground drying in the photo.
While the glue dries, I decided to apply the first coat of white flex-seal to the side and roof panels. I used a roller to coat it all over, and then used a spray can to make sure any little crevices are well sealed. I will probably end up doing a total of two coats to the entire outside.
Here you can see all three walls up, with the roof panels laying on top. The first coat of flex seal is now on.
I need to pick up some more spray-on flex seal to fill in the seams before the second coat goes on.
Lastly because I’m using a five-foot wide trailer, there is an extra foot of space on the roof next to the four-foot solar panels. This means there is room for a vent with a built-in fan! I used a jigsaw and cut out a hole, then it was a simple process to screw the vent down and seal the edges with flex seal.
I got the only Air Conditioner that Home Depot had at the time, which ironically was the same one Will Prowse tested to run off solar. It’s rated for 6,000 BTUs which is extreme overkill and should be quite efficient for the tiny space. I love that it has a loud but low-wattage fan. A loud fan is a must have for me if I’m going to get any sleep.
I used a jigsaw to cut out a box in the front wall to fit the air conditioner. I also made sure to leave enough room underneath the AC for the toolbox. Next I will add wood at angles to make the overall shape of the front of the trailer more aerodynamic.
Back Door With Digital Lock
I wanted to have the entire back wall open as a door for several, reasons. First it’s a nice big open space for loading cargo and materials into the trailer for transit. Second it’s much cheaper than installing the typical doors people use. I cut a hole in the 3/4″ plywood to mount the lock directly onto the 2×6 frame on the inside of the door.
This slides perfectly into the frame of the trailer, with adhesive weather stripping forming a seal all around the opening. I also installed a pair of gas pistons to lift the door and hold it open. This was tricky and took a lot of trial and error to get them positioned perfectly. Overall I’m very happy with the way the door turned out.
Initial Performance Data
I drove the trailer to a campground about thirty miles from my house. As you can see it’s not yet very aerodynamic, and yet I got about 30 mpg which is barely lower than my usual 33 mpg. I was surprised it performed so well, but after reflecting on these numbers, I think a big part of it is the fact that I’m driving 55 mph with the trailer rather than my usual 75-80 mph. My car is rated for 40 mpg if you’re driving 55 mph, so actually this is probably taking away about 25% of the optimal efficiency. It will be interesting to see how it does once the shape is more aerodynamic.
Because the power systems are not yet complete, I plugged the camper in at the campground. I left the AC on the entire time we were there (with the eco mode turned off) in order to test the power consumption in a typical summer camping situation (92F). To be fair, I would never leave the AC on if I was not inside sleeping. It averaged 175 watts per hour across the whole weekend.
Based on similar work published by Will Prowse, it seems logical to expect about a 50% decrease in power consumption once the trailer is well insulated. Since I will only be using it about a third of the time, it also seems reasonable to expect a further 2/3 decrease in daily consumption. Therefore I estimate that once insulated, I will average about 1200 watts per day for the AC during warm months. The heater is rated at the same wattage.
Since this test data comes from an extreme temperature day, it seems reasonable to expect that this will be the high-end of the annual HVAC daily wattage, and therefore that the 2kw battery bank will still be plenty for my daily needs. I’m not trying to have an overly glampy camper, I really just want to be able to be comfortable when I’m sleeping.
One really interesting takeaway was feeling the temperature of the walls inside and out. The white walls felt cool to the touch inside and out even in direct sunlight. The unpainted wall however felt hot to the touch both inside and out. I was surprised at how significant the temperature difference was just from painting the outside white. I will definitely make sure to finish painting the remaining rear wall as soon as the paint is back in stock at the store.
I had been debating whether or not to add jacks to the trailer, and as I walked around on it installing the bed, I noticed a line which I could not cross without it tipping over backwards. So I decided to add jacks.
The electric jacks I found need a 2.5 inch hole which seems fine going through a 2×6 but I decided to stack two 2x6s just to be safe. Since the trailer is five feet wide, I cut the 2x6s to six feet, meaning there will be a 6″x6″ square sticking out each side. I cut holes here to mount the jacks. I bought a set from harbor freight but these are the closest equivalent I could find online.
I cut the beams to size and wood glued them together, then deck screwed them together in eight places. I used three 120mm bolts to mount the beam to the trailer’s structural cross-member just behind the tires. This should be perfect for making sure it won’t shift around or tip over once it’s set up.
I tested the design by pushing the structure around once it was up in the air and it all seems very sturdy. Before I installed the jacks, I jumped on the ends to see if there was any give, and it was all rock solid. These jacks are each rated for more than double the weight of the trailer so I think it will work perfectly.
I used some locktite to attach a high precision bubble level to each jack’s base as well as to the trailer’s tongue. This makes it easy to level everything out. I ran power from each jack to my main 12v distribution panel. (see below) I also attached an inline breaker so the jacks don’t receive power if they don’t need it.
The trailer’s frame wiring includes a special ground line I ran to all the lights and frame segments because the manufacturer just expected the ground connection to magically travel through painted joints which obviously doesn’t work. So when I wired the jacks, I also connected the ground from the 12v distribution panel to the ground line I had run for the lights and frame. This is one of only two places where wires run through the exterior of the trailer. I drilled two tight holes for the wires, then stabled them on both sides of the wall and filled the holes with locktite. I will also add a coat of clear rubber over that once it dries. This should form a very good seal while also preventing static problems in the low voltage system that could otherwise arise. I will probably add some kind of grounding strap in the future. There are going to be a lot of mixed voltage systems with thousands of watts of batteries inside, so we want to avoid ground isolation as much as possible in order to prolong the life of the electronics.
So I made several errors in my design based on a mistaken assumption. On this trailer, the wheels are not halfway down the bed. They are more like 2/3 of the way to the back of the bed. This means the torque moment on the tongue is basically maxed out at a proper 60/40 weight distribution. I designed the layout to be 60/40 with a centered axle so too much of the weight was forward of the axle. Also, most of the heavy items which will eventually be in the rear are not yet installed. (Ie, the fridge and other appliances.)
Adding jacks behind the wheels and lifting the trailer off the tires to level it means that the fulcrum moves even further back. I remember seeing the level on the tongue showing a different lateral angle from those on the jacks and feeling like I must have installed it crooked. In fact, the tongue beams were torquing.
Combine that with the fact that the tongue jack comes pre-assembled with some play, and therefore exerts a lateral torque on the already stressed tongue beam and you can guess what happened when I stepped on the tongue to install something on the roof. The tongue beam twisted where the jack was mounted, and then bent 90 degrees out at its center to release the tension.
I removed the toolbox from the front and the cargo from the inside before lowering the jacks. It was still pretty heavy to lift the trailer, but I was able to do that and leverage the tongue jack to bend the beam back into place. I used a car jack to lift the tongue at the front. Without the weight of me standing on it plus the cargo, plus the longer fulcrum, the trailer was suddenly content to stand on its own. But, I knew the beam that had bent was fucked.
You can see the steel that buckled where I bent the beam back into place. Luckily, the beam was the only part of the trailer that was actually damaged.
I called the manufacturer and they sent me a replacement beam as well as a new cross member for the tongue. It wasn’t very hard to replace the beam, and I added the new cross member to the bottom of the two beams so that there were now two cross members between the beams.
One of the lag bolts for the tongue jack bent when it hit the ground, so you can see I also replaced that with another bolt. I have been very careful to frequently check the tongue weight to make sure it is easy to lift, and that the jack is not tilted at all.
I will probably not be using the rear jacks to lift the trailer off the ground unless I have a flat tire to change. I think they will basically only serve as theft prevention tools as this point.
The second cross member really ought to be included in the normal design of the trailer. There is basically no way this beam could have failed with a second cross member in place. The bottom side bent out, and that couldn’t happen if it was designed like this with two of them, rather than with just one on the top. The part number for the cross member describes it as “spare tire mount.” This seems like such a stupid design. I will have to be careful not to break it again.
But all is well now!
Back at home, I decided to run some tests to see how effective the insulation was at reducing the energy requirements. First, I put temperature sensors both inside and out to log the uninsulated temperature curves and compare the percent kelvin difference.
First let’s look at the data about the thermal performance with it just sitting there with no heater running. As you can see above, the lines are basically the same shape. In fact, with inside/outside correlation of 96% and a beta of 1.0. There is obviously a difference between the two spaces, but they track precisely together. The goal of insulation is to make the inside line as flat as possible. A beta of 1 is basically the worst possible beta for insulation. This means it’s literally not working at all. So we have a lot of room for improvement. Let’s see how low we can get that beta!
Now let’s see how much energy it takes to keep the space inside warm without insulation. My heater and AC are both 500 watts so it should be a roughly equivalent test in terms of the calorimetry. I ran the heater inside and measured how much power it needed to maintain temperature. At 55 degrees outside and 70 degrees inside, it took 200 watts to maintain the temperature for an hour. This is roughly equivalent to the AC’s power consumption as expected.
Since I framed the trailer with 2x6s, there is a 1.5″ gap between the exterior walls and the future interior walls. (2x6s are actually 1.5″ x 5.5″) This is the perfect depth for sheets of R-6 polyisocyanurate. It simply needs to be cut to size and put into place. Next, nice sheets of plywood will cover the interior walls.
As you can see, despite even colder temperatures, the interior temperature stays much flatter with insulation. We now see an inside/outside correlation of 95% with a beta of just 0.77. This is a huge improvement over the uninsulated values, from just an inch of polyiso insulation.
I ran the same experiment again once the insulation was installed. I ran the heater for an hour when the external temperature was 55 degrees. Heating the inside space up to 70 degrees took just 120 watts, a reduction of 40%. Hopefully when it’s warm out, I will see similar efficiency improvements with air conditioning.
The biggest thing to do here is just cut the hole for the shore power and then assemble all the pieces. There is a 12 volt system and a 120 volt system. Let’s start with the 12 volt system. This system runs the jacks, surveillance, and the accessory ports.
I am using this 12 volt distribution panel. I am using a single high current relay to switch automatically between a shore-powered supply or the main battery supply. I chose to use a very large shore-powered supply because I need 30 amps to run the jacks and I want to be able to run them off of shore power in case the battery is ever dead.
Wires run from the distro panel to things like the linear actuators, jacks, ventilation, and eventually the future water pump, and other 12v accessories.
The generator plugs in through a shore socket on the outside of the trailer. This means it can stay hooked up when not in use. If shore power is available, then we simply unplug the generator and plug the shore power in.
From the shore socket, power runs to a power strip which serves as a shore bus. From here, the lithium bank can be charged from either shore power or the generator. (I will add a link to the lithium bank when it becomes available for sale. I bought it on an Indiegogo and they are not currently for sale. In the meantime, something like a Bluetti 2400 would be equivalent though this doesn’t charge as fast so I would wait for the new one to come out or else buy two of them.
An automatic transfer switch defaults to shore power if available, or runs off the lithium bank if no shore power is available. This switch powers the chassis bus which is a special kill-a-watt plugin strip allowing things like HVAC or lighting to automatically run from the most appropriate power source. Also in between the transfer switch and the chassis bus is a UPS to smooth out the transfer and prevent power loss or surges from reaching sensitive equipment.
Main power is produced by two solar arrays. Each array contains three 100 watt panels mounted to a tilting frame. One of the two arrays is mounted to the roof. The other is stored on the roof and then deployed on the ground.
I had already purchased the cheapest ceramic heater I could find, but I doubt I’ll need that in such a small and well-insulated space. It uses about the same 500 watts as the AC, though neither seems likely to be on more than a 20-30% duty cycle with how small and efficient the space is.
I have also had many people recommend the Mr Heater which could come in handy if I decide to go ahead with my tentative plans to eventually build a portable sauna. I will probably buy one of these as a backup heat source just in case.
I should probably add that I have a lot of camping gear already, including cold weather gear. If you’re going to be camping in cold climates, make sure you are prepared to survive.
- I’m using a miniature combination fridge/freezer. I especially like this one because there is a separate freezer door.
- I decided to get a small ice maker for drinks and for the cooler.
- Rice maker
I have done a lot of experimenting with various methods for making my own water. I plan to upgrade my current pump to something with a little more volume.
I’ll probably get a nice multi-stage filtration system as well. If I do that, I’ll likely also add an outdoor shower and some kind of large potable water holding tank. (Possibly something wide and flat underneath the bed of the trailer)
I purchased one of the top rated portable toilets, and a small popup tent to serve as an outhouse. I intend to store these in the trunk of the car rather than the trailer, so as to keep any scent far away from the living spaces.
I will miss having the bidet from home.