Like others have posted, if we wanted good milage we wouldn't be driving a 6 ton box on wheels, towing a toad. Initially I was going to keep gas milage records, but than figured it is what it is, so I don't. Just got back from a 1000 mile trip thru N.C. and Tenn. , and the money I spent for gas would have paid for 2-3 nights in a motel. Instead we spent 9 days camping in some beautiful campgrounds, four of which were next to a river.
If you have to worry about a mpg one way or the other, you need to re-think your set-up, and what's important to you.
Grumpy