Re: Winshield wiper on bed cap?
Look into the Mercedes Benz SINGLE center mount wiper used on 190e from 1984-1993 which sweeps the entire width of the windshield. (perhaps available in other MB car years, I have owned 2 and am familar with it.
The motor/gearbox has a cam sweeping design which amazingly covers the full window width. The entire mechanism is about 5" high by 12" wide, not geometrical. Next time you see an owner in a parking lot have him demonstrate using the washer - which is something else you need.