Best way to keep the sun's heat from the front away ?

harold1946 wrote:
If the object is to keep heat from transferring through the glass the covering has to be done on the outside no matter what material is used.

Glass is not magic. Heat that enters can be reflected back out the other direction. A reflective foil insulation used on the inside will just reflect the heat back out of your coach. In addition, the inside reflective insulation is easier to install by sitting it on your dash and will remain clean rather than exposed to the outside elements.