I had looked at using insulation foam and PMF (Poor Man's Fiberglass) in the ttnt trailers foamy fourm and the build is possible but doesn't give as good a look and requires interior cabinets be used as structural componets but I believe it would be durable and easy to maintain once built. Unfortunately I fear I just cann't get myself to believe I have the skills to pull it off, so I did something I was more familiar with but just as impossible. I live remote and do not have a shop. Building projects outdoors and with no large flat surfaces is a challenge. I decided to use pannels made of foam and plywood but they were too expensive for me to afford. Even to build them looked to be around $75 to $100 per 4x8 sheet. I looked for cheaper materials than plywood, bhellout none looked any better. I wanted something more substantial than just foam that I would have to plan a wood insert every where I wanted to attach something. I finally found something but every person I talked to told me I was nuts and it wouldn't work because they attract moisture and fall apart if they get wet. It was interior doors. They weigh less than plywood/foam pannels but more than foam. Using the PMF completely waterproofs them. They are square and preassembled. I have been able to buy damaged ones really cheap and even new ones for around $30. Another thing I found is metal attracts moisture and expands and contracts much more than wood, so metal fastners are destined to fail. Wooden dowels work much better and with todays glues hold better. Doors with square edges are a breeze to dowel together and if you need to attach something in the middle take a 1" hole saw to one side, glue in a 1" dowel, drill some 1/4" holes around the dowel and fill with spray insulation foam, you won't be able to break it out even with a hammer. If high load surface simply glue on a piece of thin plywood like 1/4" and you can jump on it without breaking through. Thoroughly coat it with PMF and outdoor paint to waterproof. Mine has lasted over 3 years now with no problems and lives outdoors in southern Utah. Sorry for the long post and lack of pictures but I'm getting to old for all this new stuff I have to learn.