Is weight of the build-out material/furnishings a concern? I imagine that while wood shelves, furnishings, etc. are sturdier and more available, they weigh more. Is there a material that is strong, safe, easy-to-work-with, and economical?
Well, Vibranium would probably be the Gold Standard.
I'm thinking more down the lines of aluminum tubes, I-beams, etc. Even something like building a jig to turn sheets of aluminum (such as from a roll of flashing) into fan-fold/accordion components with a greater strength-to-weight ratio.
I also would love to hear any ideas for affordable composite construction. I'm not sure of the real-world practicality (or environmental suitability), but I was toying with the idea of using spray insulation on wire armatures with strategically-placed "hard-points" in prototyping different configurations.
I'm on the road for 6 months of the Year at least. I live in my truck. I haven't modified it very much. There's a cot in the back. I can cook and hang out in the back when it is raining. I can hang out in the front as well. I used to have a built-in bed kit in the back of my truck that I made myself. I found they were too heavy and unnecessary. Since I am not sharing the back with a partner anymore I've decided to go with just a cot, crates and boxes - and weight savings helps a lot on gasoline. Good luck on tricking out your van.