Well built 4x4 crew cab diesel pickup. You can put a camper on the back, or even just a fiberglass shell. Small lift with some good tires and they will get through some nasty stuff.
Throw in an aux fuel tank and you can get 100 gallons without much trouble. From wa, worry about fuel somewhere near Tx or Ohio lol.
Those unimog motorhomes are sweet, but $$$$