It would be educational to go to some dealer lots or RV shows and crawl under a few Class B's. The limiting factor on rough roads isn't only the ground clearance of the van and the skirting, it is also all the other things that are usually stuffed underneath Class B's because there is no other place to put them (tanks, generators, batteries, water lines, etc.).
I like some of the Fit RV videos because he crawls under the van to take pictures. Here is a good one for the Travato. Watch this video starting at about 17 minutes. I have been on lots of National Forest Service Roads where I would be pretty nervous dodging boulders, ruts and mud with a van that looked like this on the bottom.
http://www.thefitrv.com/rv-reviews/the-59k-a-new-travato-our-new-review/
