We have a class C on a F450 truck chassis. The option to order the truck with 4 wheel drive was a big deal for us. We don't use it a lot and we definitely can not go off roading like with a jeep or expedition vehicle but it's great to have. We don't worry much about getting stuck and can boondock with ease. The 4 wheel drive option on a truck chassis is about $1,000. After market on a van chassis runs between $10,000 - $20,000.
The truck chassis is very stable. It also has a heavier suspension, ball joints, tie roads, etc. and is rated at 16,500 GVW verses 14,500 for a van.
The power is probably about the same because it uses the same engine. Gas mileage might be slightly less with the truck because it weights a little more.
Maintenance is the same but it's easier to work on because there isn't a doghouse between the seats. All work is done outside the vehicle. Lack of a doghouse also keeps the cab area cooler and gives the passenger more foot room. It's easier to move from the cab to the living area of the motorhome.
The only disadvantages are that it's slightly longer than a van chassis RV and the ride may be a little harsher.