So we tried proper camping on the Great Lakes Mistake rally. It was fun and all but we found it taking too much time for setup/teardown. If you are just sleeping in the car that might make it easier but at the same time you might find yourself really wanting a shower after a few days in a crap can without A/C. (Assuming you are roughing it)
If you have a van or like a long roof station wagon you could probably comfortably sleep in it, park in a Walmart parking lot or something. Some states will let you sleep at the rest stops but I would check laws state by state before doing that. Worst they would do is probably tell you to leave.
Count yourself lucky that you have a vehicle large enough to even consider such a thing, our X1/9 is hardly big enough to even sit in.