We had shades made that snap on to the outside of the coach and cover the windows. I've considered using bubble wrap between the cover and the glass to insulate the glass. Obviously, bobble wrap on the inside might cause the glass to overheat and discolor the plastic film between the glass, so don't do that.
Some friends have used tin foil on the inside of the windows. I'm not so sure that's a good idea since the heat buildup could damage plastic film between the glass as discussed above. Tin foil on the outside would work but sure would look trashy.
