Building my own truck camper

2x4's will be too much weight.. most rv's are built using 2x2's and 1x2's. paneling on the inside and 1/4 or 3/8" for the lower walls and bed area. i would go to 5/8" for the bed area and floor. and use at least 1/4 for the roof, a better choice would be 3/8 or 1/2 so you can walk on it. laminating two 1/4" sheets after getting the first curved and screwed would be the best method. i would recommend a thin sheet of foam and a layer of paneling, a radiant barrier then your skin. either fiberglass or metal. use foam or fiberglass to insulate your walls. you will need to split r-13 insulation as it will be too thick. the roof use 2x3's or build trusses. insulate and use a radiant barrier. over the plywood. use fiberglass, metal or rubber on the roof. if using rubber, insure it is glued down very well. or it will lift and possible separate. you can pick up the windows, vents and doors from a rv salvage company. along with your lights and plumbing fixtures. sometimes they have the battery charger voltage regulator units available. they should have used solar panels and charge controllers. along with your shore power cables. pex plumbing is pretty much standard now. buying the tool is worth it, to get the fittings and clamp rings tight. look up some designs, they should have examples on building the dinette and drawers. or buy some used kitchen cabinets. a couple of staple guns are your best friend for building a rv. structures use screws and large staples 1-1.5" wide. 3/16- 1/4 staples for paneling. if you know how to weld aluminum, that will save you lots of weight compared to a wood frame.... remember weight is your enemy. you will go over your 1500 lbs, real easy.. have fun and post your progress.