Boy Wonder and I have used my '62 Suburban for deer camp a few times, and we've also slept in the back of it for out-of-town car shows. As said earlier, it was basically a rolling tent.
We have an air mattress that just barely squashes in between the wheel wells. Don't latch the rear doors at night, and you've got your escape for when nature calls. Crack the side windows for ventilation.
One thing that'd make it a little nicer was if we had cots above the wheel wells, rather than an air mattress between them. That'd give us a little room to get dressed, and we could sit up, etc.
I know where there's a '64-'66 panel that was used as an ambulance at one time... it has a raised ceiling on it and rear barn doors. It'd be a great tow rig and cross-country hauler for me and the boy, but my wife would probably not enjoy it as much. If it's still there in a couple years, I think I'll try to get it. Too many projects, and not enough storage space right now.
-Brad