I get about 20-22 mpg usually in my toyota, and it has a made up bed on top
4 whopping cylinders on Toyota RV's. Talk about great getting good MPG. Also I have a very light foot on the pedal. I followed some MPG advice on Livingpress.com and I now get 22 MPG! Not bad for a home on wheels.
If you wanted to import a DOT/EPA modified version, would it be subject to the chicken tax, which so far has done a pretty good job of keeping out the vans these are built on?
I don't think a complete RV would be subject to chicken tax as it's a passenger vehicle.
Trucks were subject to it and there have been a number of ways manufacturers have got by that. The Sprinter is shipped as a kit, the Transit Connect is shipped with a back seat which is scrapped, and Japanese trucks used to be shipped incomplete.