Look at the work by Kach22i.
http://ecomodder.com/forum/showthrea...1-a-19525.html
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A Bonneville style spoiler and half-tonneau are considered 2nd to an aerocap.
Here's my take on an air curtain:
A time attack style diverter to scoop air and throw it sideways. Then a winglet that constitutes a converging duct that redirects the air into a [fraction of an inch] slot the height of the wheelwell. The back edge of the winglet would be matched to the locked wheel and tire, not the fender opening.
Put you tool box at the back of the bed like this:
Works as a spoiler. You can add tumblehome to the sides.
edit:
For comparison, the NASCAR Camping World racers use a ducktail spoiler. Same height as an aerocap truncation, just without the smoothening.
https://speedsport.com/nascar/martinsville-truck-penalties-announced/
See all the turnbuckles? There's a lot of force involved. A [tool] box would be inherently stiffer than a flat plate.