CTENG,
I used to work for a guy that modded out his cargo van for about 1K, avter paying I think 3K for it at auction. It was 2 years old when he bought it, it was from the City of Sacramento yard, had something like 40k miles on it.
he made a box out of plywood, about 18" deep, that was just the right size for a twin mattress. He put a lid on it, and set the mattress on top of the lid, with a lip around it to keep it from sliding off. He used the hydraulic risers from a minivan's rear hatch to lift the lid, and keep it up, and used the 40"x72"x18" (rough guess) as lockable storage underneath. He also built shelves out of angle iron on one side, with the outside edge of the front peice angled up. They were the exact width for milk crates, and the lip would hold them in. He installed a high output alternator, and ran 2 batteries. He had a dorm refrigerator running on an inverter off the batteries, and he could leave it overnight without running the vehicle and it would still start inthe morning. I think he also had a microwave too, but about the time he got that, he moved.
If you're interested in pursuing this, I can draw some pics if this wasn't clear enough
