Insulate my windows with fiberglass?

I have some windows that I want to insulate at night during the winter. I have energy star windows, thermal drapes, and cellular blinds and those plastic window film kit things, but I want to reduce my heating costs even more.

So here’s my idea. What if I took a bunch of fiberglass or mineral wool insulation, wrapped it in a bunch of plastic, and shoved that in between the window and blinds at night, possibly filling in gaps between the plastic and the the window frame with other material, and possibly secured on the inside end by a board or something? Then I would probably take it out during the day.

I’m wondering

1. whether you think this would significantly affect heat loss through
   the window,
2. whether it would cause any condensation problems,
3. and about any unintended consequences I might be missing.