sprinter window insulation Kit ?

In past years when we still traveled in cold climes I would cover the windows with heat shrinkable window film. It was available at the local hardware store. I would apply it to the inside window frame and that would leave about half an inch of dead air space, of course you can not open the window. It made the rig a lot warmer and helped a lot with the condensation problem. When you hit the film with a hairdryer it shrunk up tight and was nearly invisible. The film is cheap enough that one can just throw it away come spring. One box lasted several winters.
I wouldn't try putting it on a windshield. :)
Wayne