Pulling any high walled RV with a gas engine means 8-10mpg. You are trying to pull two sheets of plywood through the air at 65mph. It's a lot of work, thus lot of fuel. If you are not willing to accept 8mpg, then stick with low walls.
Many RVing familes simply do not tow many miles, like less than 2000 miles per year. Doing the math of 2000 miles at 13mpg and 8mpg and $4/gal means less than $400 per year. That is fairly small compared to conveniences many TT owners enjoy. TT's offer far more storage and shorter setup/take down times.
