02 - Build The Walls
So.... this is a case of do as I say, not as I have done. Building the walls flat would be much easier and produce much better results than building them in place. Also, I will say this many times, I am building a prototype here. My intentions are not for this thing to last forever. Otherwise, I would have only used marine grade plywood. However, that is expensive and difficult to get where I live. Since I do not store this outside, it will still last a very long time using off-the-shelf plywood. The plywood core is 1/2 inch plywood, and the inner skin is 2.7mm underlayment. Using the internal skin you cut in the first step and a flush trim bit in a your router, you are able to cut the outside shape of the wall. Internally, the voids are filled XPS foam insulation.
For the floor, I used a piece of 1/2 inch plywood. The mistake I made here was that I should have extended the floor on the front and back to match the thickness of the cross spars and ceiling. While this ultimately worked, It would have been much stronger.
As you can tell, campers are typically built from the inside-out. This is the way manufactures construct their trailers. Crawling in and out of these little trailers to do finish work is very difficult. Since this was really a prototype, I did not do much finish prior to assembly. This was a tradeoff that cost me a lot of time latter trying to make things work. So... try to think of your project as modules that are built on the bench and attached to the project.
The cubby floor is used to hold the the walls in place just for the mock-up.
The plywood on the inside walls is very thin. Just a couple mils. I was able to purchase this at a local big-box store. It is about half the thickness as normal Lauan. I was able to cut the initial shape with a pair of thick scissors, then used a flush trim router to clean it up.
The cavities of the walls are filled with XPS foam and glued into place with wood glue. I do not recommend using this type of glue. It seems to never dry completely. For my next project I will be using Foam Fusion to glue in these pieces. Buying foam to match the thickness of the plywood is impossible. Also in this picture you can see T-nuts used for anchors points. I use these to tie up things like lawn chairs inside the cabin.