RVs aren't designed for aerodynamics. They're designed to be cheap to build and roomy inside. So it's easier to staple aluminum to straight 1X4s and have roomy interiors than it is to taper rooflines and have users complaining about unusable space.
Besides, if you've got $100k - $500k for a big RV, filling the tank for $500 isn't a big deal  .
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Darrell
Boycotting Exxon since 1989, BP since 2010
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin
Mean Green Toaster Machine
49.5 mpg avg over 53,000 miles. 176% of '08 EPA
Best flat drive 94.5 mpg for 10.1 mi
Longest tank 1033 km (642 mi) on 10.56 gal = 60.8 mpg
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