I've seen them on a few 18 wheelers, but you almost have to look for them. They aren't that obvious on that type rig.
I installed them on my RV along the sides and the roof. I didn't try to attach them to the rubber part of the roof. Instead, I had enought fiberglass on the edge of the roof to glue most of the airtab on that, and for the pointed end that faces to the rear I filled-in some of the gap underneath with silicone just to give it some support and keep it from vibrating in the wind. After six years, they're still there as originally fixed.