But, a good point raised--there's a high pressure point at the base of the windshield. It's not the place to vent the engine compartment.

Either the Granatelli's or Smokey Yunick, can't remember which, made a clear plexi hood for one of their stock cars and tufted the engine compartment. Claimed to have seen measureable improvements by moving components around under the hood.

Heh-heh. I'm told I can drift off and bs with the best (worst?) of them.
Anyway, turned out to be an interesting discussion, and is actually aero-oriented anyway.

Sounds like a Yunick to me. He was a very innovative person, even went so far as to install a windmill on a car to run the generator, and even hand built an exact 7/8 replica of a 1967 Chevelle to run at the races. Nobody noticed it until he made the mistake of parking it beside a factory 67. Another trick was cheating on the fuel load, he used a 2 inch diameter fuel line to carry fuel from the gas tank to the engine, giving him another 2-3 gallons of capacity. This was discovered when the tech inspectors removed the fuel tank for measuring, and someone got into the car and drove a couple of laps with no fuel tank in the car. Smokey Yunick is probably responsible for about 90 percent of the NASCAR codes where measurements are concerned.

The windmill driven generator idea running an alternator might work for fuel economy, should be enough to keep the battery topped up at highway speeds without affecting fuel economy. There would be more than enough air to drive the blades if you mounted it so part of the blade extended down into the undercar airflow, and this should have zero effect on fuel economy since that air has already disturbed the motion of the vehicle.