I think Airstream is the best going right now.
I had a 34 foot HitchHicker 5th wheel with a wing attached to the top of my pickup. It help with the wind, but was a trial and error on the wing angle. I think a lot has to do with the tow vehicle and how it channels air around the trailer - then up to the trailer to exit the air smoothly. You see some big rigs set up for something like this - let me find a pic somewhere...
Here is an example to get things brainstorming...maybe RV manufacturers could offer aero kits for the tow rigs to match the RV aerodynamics?
Lonestar:
Aero RV stuff:
Titanium:
Maybe a modified "hi-lo" would be a good base to start out with then improve from there?
