My though was the same as 48rob. Sleeping is a small part - food showers and restroom facilities are also key. As GI showers are fine, food and restrooms are probably not a concern either. Do the venues you race at allow camping? Most do I'm sure, but know those rules first.....campgrounds tend to be the same distance or farther than hotels

. Unless you want interstate side sleeping....I don't. I don't want to be within 2 miles of an interstate...
Purely from a comfort point of view, I hate hotels. I've already decided that my teardrop or an RV will be the only way I'll spend any time away from home, unless it's corporate travel where I have no control. The fleabag hotels are just gross. The hHiltons cost way too much, and they all seem to be getting worse. The oldest and least well maintained campground I've been in was still better than the worst hotel...maybe it's just expectation. But $25 a night I can forgive a lot more than I can for $100, and I've still got my own mattress and pillows. Good shower shoes are a must.
On your fuel economy question, I'm a cheater, my rig is commercially made (camp inn). Weighing I can only guess on, but I figger (sic) around 1100 pounds estimated plus gear, I lose about 4 mpg when I tow. With a jeep liberty diesel and a Subaru outback 3.6 liter, I forget it's back there. I don't baby it too much, but I don't speed to begin with....sign says 65 I'll do 70 tops. Rarely will I go faster than that...
Where are you from? Look for a gathering in your area, stop by and get to know us. It's a lot of fun to see others work and meet some really good people while your at it...