My solution is to place 3/4" rigid foam insulation panels, available at home centers. inside the winshield and single pane front windows. Cut to fit the shape. 3/4" weatherstrip makes them have tension top, bottom, and sides (on every other panel) to make it air tight and stay against glass securely.
I also put white vinyl outside on the part of the winshield that is painted black on the back side where the cabinets above the dashboard are. I also put white vinyl on top of the fiberglass cap.
Combination of these three things makes it possible to keep the beast cool even when front of coach is parked into the sun.