[Daox]

MetroMPG is thinking about doing this as well. My main concern would be moisture build up between the two windows. You'd ideally want to vacuum the space between the windows or something to get the moisture out of there. There is also the fact that doing this will reduce the VT (visual transmittance - the amount of light you get) through the opening. Otherwise, it should work rather well. Its basically the principle of the super high performance windows like Serious windows where they have 2 panes of glass and multiple sheets of plastic between the glass to create more chambers in the window to reduce heat loss.