[elhigh]

They may not be able to follow aero, but they can understand power. That "rolling bubble" of air the truck's motion generates in the bed takes power to create. The bed cap effectively replaces the bubble while requiring no energy to keep it there, and with less turbulence. They can understand using less power. These are the same guys who'll pull the balance shafts out of an engine so there's 3hp more and less rotational inertia for drag racing; they should be able to understand this.