I've looked high and low for an inexpensive tonneau cover for my truck bed to reduce aero drag, but the good ones cost more than I want to pay.
Truck caps have even more potential to reduce drag. I looked for aero truck caps, but they're all boxy and not at all tapered at the rear. Somebody could make a fortune making aero truck caps, if you ask me. I wonder why Leer and others don't make them?
Anyway, I bought a couple of pieces of plywood to make one for about 25 bucks. I'll post mileage soon.
Capitalism: The cream rises. Socialism: The scum rises.
I always thought some kind of boattail extension off the back of most cars would reduce the turbulent air flow behind the car (even for a fairly efficient car with a chopped off rear-end). Instead, you'd have a laminar flow off the trunk lid with a swirl trapped just behind the trunk that isn't interfered-with by the laminar flow (example with a <a href="http://people.clarkson.edu/~visser/research/drag/truck/">tractor-tailer</a>).
Reality is merely an illusion, albeit a very persistent one. - Albert Einstein