Originally posted by RoadKingMoe
Some time ago, a university research team put a truck in a wind tunnel, and tested various methods of reducing its drag. The results were published on their university web site. I can't find that any more.
The tonneau cover came out on top in drag reduction. IIRC, dropping the tailgate and a net only helped a little, and a camper shell actually increased drag.
The results certainly might be different with an Airstream drafting up close behind the truck, but I wouldnt' say for sure.
Simple airodynamics. If you want something to go fast it is tear drop shaped. It parts the wind and then guides the air back so it can slip through.
With and abrupt end to the body then the air creates vacuum on the back of the vehicle. That's a much larger area with a raised top shell. Car manufactures have know this for years. Take a 70's Suburban or even GM and Ford vans. They are their widest and highest at the B-piller on ALL of them and all three taper down to the rear. That taper, that is not even noticable to the average person, was worth a few points in drag CO.
Yeah the raised camper shell may help with towing a vehicle taller then the tow rig but on a Airstream I doublt it will provide any noticable improvment simply because the rounded leading edge of the Coach already does this.