We have gone to a lot of places including Alaska and back, the gravel On Top of the World Highway to Dawson City, Yukon and many national forests on gravel roads. There is not a lot of need for 4x4. If you desire that rugged I think you would rattle and tear apart a typical B interior. A B is a big investment to abuse.
However, I came very close to ordering a Mercedes Benz Sprinter 4x4 which will be shipping the 1st quarter of 2015 but it was a tad too late for my needs. Advanced RV, I believe, already has customers and will be converting for them.
There are a lot of primitive out of the way campgrounds you can get to only with a Class B (or a truck camper you don't desire) mainly because of 24 ft. restrictions. But I haven't found the roads onerous to traverse other than maybe the width which could give truck campers and small Cs the willies.
