[Big Dave]

Couple of thoughts on your initial post.

Yeah, a tonneau would be easier to make with the materials on hand but (in my experience) an aerocap is more effective.

For my truck a hard, flat tonneau netted a 1.5 MPG improvement over an open bed.

For the same truck, my old crude aerocap (see avatar) showed a 3.0 MPG improvement over the open bed.

Name your poison.

Like you, I live in the Midwest where the wind can mortally howl out of any direction and farm fields offer no shelter. With either the tonneau or the aerocap, I never had any problem with crosswinds (the 7,500 lb truck overwhelmed the problem). I haven't heard anything from any of the site's aerocap builders about crosswind effects.

Whichever you use, I'd advise bolting the cover to the bed. Last spring a 50 MPH crosswind got under my tonneau and broke TWO C-clamps and I had to chase my tonneau 50 yards out into a muddy corn field.