Aerodynamics & Diverting Wind Resistance ?

I like the plexiglas idea or louver idea already brought forth. New cars (and trucks) have shutters that close and open. Open to cool the coolers and close once up to speed to reduce drag. Something like that in the 1/4 could maybe make a difference. They’re also super thin and brittle. It wouldn’t take much to divert the air. And also stated, smooth finish is huge. I had a Jeep Cherokee years ago and I had to repaint the roof. The difference between unsanded primer and when I finally did single stage was nearly 2mpg.