[aerohead]

Originally Posted by kach22i

This is totally a KISS method, might try it on my own truck. Is it crazy or what?

Modified a random image off the Internet, should work on any pick-up truck.

Cant corrugated plastic in 10-degrees from top and both sides, with tailgate down.

Automobile 2 - Odds And Ends Photos by kach22i | Photobucket


Might have to put a cargo net back there, could be trouble otherwise.

Inspiration was this:
Automotive Aerodynamics: Drag Area – Size Matters

I think that it will definitely show at the gas pump.
As long as the trailing edges are round about where Mair's boat-tail profile would be,the air will separate at the tailgate area,then swirl into a captured-vortex;stuck against the tail,with the outer air streaming by.
It's that outer air which will have a chance to decelerate to a higher pressure before it does break away,which will raise the base pressure back there.