Hi,
Welcome to the forums.
A small toad is going to be a better fit than a cycle if planning to boondock. Gravel roads are NOT often fun on a Bike.
I'd define my goals a bit better.
Diesel used to be more reliable than gas--but not so any more, and maintenance on a diesel is often sky high. It also boosts the purchase price, sometimes from expensive to outrageous. Plan on 6 miles to the gallon--and then look at the price differential on fuel.
If boondocking a way to have reliable power is a must have. I chose the solar route for that.
If, on the other hand, campgrounds are your pleasure, often you can rent a car locally.
A small Class A often has more storage than a Class C.
While it is possible to live frugally in an RV it may not be much fun to do so.
It may be a good idea to rent an RV for a month before jumping out of the frying pan.