[aerohead]

A local tile floor contractor has an Econoline conversion with 2-ft roof extension.Even with his wet saw and all his gear,he gets blown all around on the highway.
*If you could do some sort of pop-up top as already recommended,it would hurt you the least at the pump.
*If you must do a rigid top,then ideally,you'd want a bulbous nose as you'll see with some trailers ranchers use hauling livestock.This is best when driving into quartering headwinds.
*A 6-inch radius all the way down the top edges will reduce roll moments in a crosswind and gusts.
*And if you can teardrop the roofline towards the rear as Don Bur has done with their semi-trailer rigs,this will help the air to think that your RV is actually a bit smaller.
*As mentioned,the Aerodynamic Streamlining Template is created to help with this part of the design.The new roof would want to look like that of the 2014 Corvette Stingray but with a more complex windshield.