ktmrfs wrote:
My next step is to make something more permanent. Went to TAP plastics and had them cut me a couple of pieces of plastic to try for a double pane window. Not a bad price and they did the radiused corners. Will be trying it to see how well it works, and if it works as expected will do all the windows.
Along this same line (permanence), foam board works exceedingly well. Of course, it blocks light and the view. That may not be a consideration at extremely low temps at night, in Winter. You can also use a second interior panel of whatever material as a passive heater. Allow intake and exhaust space at the top and bottom of interior panel. If the window faces direct sun, you will generate considerable heat from that window, even in very cold weather.