If you're worried about gas consumption, maybe you shouldn't be an RVer. I rarely did accurate checks, but our 32' box got about 8 mpg. Filled it when it needed it. If the trip budget got tight, we'd stay in a CG longer than originally planned and maybe shorten a trip.
Our previous rig was a 26' Class C with a caburetor-equipped 460. That go about 6 mpg at sea level and about 4.5 mpg at altitude. The EFI on the V-10 got consistent mileage regardless of altitude.
In the end, it was the combination of high CG fees and high gas prices that ran us out of the lifestyle.
