Indie dog.
The finished inside dims going to be the size of a full-size bed (52inch x 76inch...roughly..the framing will make it an inch or so narrower, but should go un noticed)) plus an extra foot at the bed (for shoes n such) and an exta foot or so at the head for storage. the bed is going to be split in 2, lengthwise. one half will fold up against the wall and will have a table (for eating, writing, maps, etc) that folds down off the bottom. the other half will stay put, and serve as a bench. Underneath the bench/bed (will be about 12" off the floor) there will be a long drawer that will house either storage or the "kitchen".....It will be accessible when the door is open, or by lifting the bench side up on a hinge...if that makes sense. The door will be the entire back face of the trailer, and will have an awning that covers it in the event of bad weather.
I think I'm going to opt against going wider that the frame is now....partially because I don't want to complicate the project and add cost for materials, and partly because I want the body pretty narrow so that I can accomodate outside storage above the fenders (thining of moving the spare tires there as well as the fuel cans and maybe some more storage boxes)