As previously noted, Jeeps. I am still two years,three months, 10 days and about 18 hours from that kind of life, but have still researched, not that I am in a hurry or anything but, if you are driving a big Class A, you are already limited to parking lots for camping. A 2WD is going to severely limit where you can go when you get there. I can't imagine going to CO, MT, UT, WA,OR etc. and NOT being able to go into the mountains. 4WD will expand your horizons beyond the tourist traps. I live in MT now and my 4WD pickup set up for light off-roading is so much fun. I think of like Moab UT and if you don't have 4WD, you will miss about 70% of the potential fun you can have over a week or so. There are a lot of places like that in Colorado also and most mountain states.
Go look up Moonflower Road in Moab and take it beyond the pavement or any number of places along 70 in Colorado or the four corners area or even the frontage road along I-15 in between Butte and Helena MT or the road from I-15 from Bernice MT over to I-90 or Tizer lakes in the Elkhorns south of Helena MT and on and on and on...