So far the research I've done. The Toyota mini RV, is the winner! I have found they range from 18 to 22 mpg. The downside is they stopped making them past 1994. Still, they are fairly cheap, but usually need refurbished. You have to count the cost. A brand new class C for $30,000 to $80,000; depending on year, make, and model. OR. You can buy an old Toyota for around $9,000 and put $5,000 of work into it. You come out the other side with a nice RV, for around $14,000, that also gets 18 to 22 mpg. I think that's better than paying over $30, 000 for an RV that gets 8 or 9 mpg. Of course the Toyota's are smaller, but they have all the necessities. Depends what you want it for.