[aerohead]

One consideration is,that even if you get one,your drag will still be higher than any pickup truck (Cd 0.38-0.45).And that's with a roof.
The Sprite's windshield is the culprit.
A spyder half-bubble screen and head fairing could get you to Cd 0.31,but you'd be required to wear goggles,unless the screen was laminated safety glass.They're not available.