For us we got a B+ to aid in moving thru the wind. Much like the aerodynamic trucks you see on the high way. Just think of a big sail with the standard c. we get about 9 mpg pulling a towd (hyundai elantra 2800 lbs) I run a scan gauge and mpg can vary on all terrain, have had 10+ on the flats even towing. The v10 is the common engine, but I wish there had been a diesel option as it just seems to run out of everything on long pulls and high altitudes (denver). Ours weighs in at around 13000 lbs as we dont travel with a bunch of junk or full water tanks. it is a 28 ft winnebago aspect.