I will second Whiskey's 4x4 van suggestion.
I'm a school bus driver and I've driven everything from the cut away vans up to the 40'. One thing they all have in common is really stiff suspensions. The body, frame and suspension move more as a unit, so going over anything bumpy throws the bus back and forth hard.
Tire choice on a bus would seem more limited than for a 4x4 van.
Buses are almost 8' wide, not narrow, W I D E.
Buses don't have much of a turning radius and some have a lot of tail swing making tight turns, three point turns, etc. basically impossible.
Around town, we route our buses based on if they can fit or make a turn. We like turning left more than right, because left turns are sweeping versus 90 degree right turns.
The shorter the wheelbase, more stuff it can go over. Buses ride low and anything other than a cut away van is going to have a much longer wheelbase.
A bus is basically a truck with a bunch of safety stuff added on. That also means the electrical is a mess due to the extra lighting, stop signs, crossing guards, emergency exits, entrance doors, etc.. Many of these extra systems can cause starting issues. Rocking and bumping a bus around might just beat that wiring up, and the last place you want an engine problem is out in the wilderness.
Diesels don't like to idle, they like to work. They like to pull. If you're going in the back country, I'm not sure how a diesel would work with going slow a lot. I don't know that it wouldn't work out, just thinking out-loud.
Plus, IMHO, I think a raised 4x4 van looks very cool! I like the ones with the deck on top that people pitch their tent on.
Best of luck.