wow! looking at your mpg, can see why you're looking for a new car(saw your thread). since you're going to get something else soon anyway, why not try acetone. but, don't know if it would help an untuned vehicle.
would help more, no? I heard that the way it works is to keep the gas from evaporating. So maybe the only place it would NOT work is on a Prius with those funny gas tanks that keep the fuel from evaporating and hence have the same effect as acetone. Correct me if I'm wrong.
Welcome to GS! Someone made a nifty "sloped" truck bed cover for their truck, but I can't remember their handle. It looked 100% retail to me. Maybe they'll pipe up. I would search the Garage for similar trucks and see what they did.