[Big Dave]

Another idea. Gap seals. Outfits that make aero mods for light planes are big on gap seals. Most aircraft panels are faired or at least fishscaled, but the flaps, ailerons and vertical stabilizer have gaps. They claim increased speed at level power settings.

Those clearly do work on 170 knot (200 MPH) aircraft but they may not be as effective for 70 MPH ground vehicles unless you have egregious gaps. The cab-to-bed gap on some pickups get overly large.