It is pretty tough to project a good effect from the truck with conventional trailers, and much worse with something like a sailboat.
The distance between the two rigs makes them behave largely like two separate rigs.
If you only lose 3 MPG towing I'd say it is not a good pursuit in my opinion. Better to reduce the truck as slowmover says, and see what that nets you. I would go with a full aeroshell.
Nice toy by the way, I love sailing.
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2007 Dodge Ram 3500 SRW 4x4 with 6MT
2003 TDI Beetle
2002 TDI Beetle
currently parked - 1996 Dodge 2500 Cummins Turbodiesel
Custom cab, auto, 3.55 gears