In our little type C we have averaged 12.29 mpg over the course of 11125 miles. Most of that is secondary roads, as we both hate to rush. That and in truth most state highways are actually in better shape than the slab. The Interstate system is just horrible in many areas. The RV is on a Chevy chassis, and has the gas 350 V8. No problems at all keeping up with traffic, and it's super easy to drive.
We've taken a couple major trips and many shorter ones since we got Thing. It's our first motorhome, but probably won't be our last.
Can't wait to take the cover off and make our first trip of the season!