So sorry that I don't have a good photo.I want to see/hear more about this window solution! How thick is this corrugated plastic? 1"? Where do you use the gaffers tape? (surely not to affix to windows). Magnets to hold to window frame? Do tell!
This is the coroplast stuff. 1/4" thick and super lightweight. I considered making our shower-walls of it but it's a little to light-weight for that. (Used corrugated Lexan instead - almost as light and amazingly strong.)
Reflectix taped to the coroplast with gaffer's tape around the edges. If not familiar with gaffer's tape, it's much cleaner and stronger fabric-based tape than duck tape. You can get gaffers tape in myriad colors. We went with black or dark gray or something like that; but you could do white to be more subtle.
Then tape magnets around the edges with additional gaffers tape. That can be done with "tabs" where they hang out a bit if necessary. The goal is that there ends up a 1"+ gap from the Reflectix to the window. That space seems to be what actually insulates.
The final product was completely light-proof from the outside and white on the inside - helping to make the space look more spacious. And the insulation function was surprisingly good. The coroplast temp was always moderate; whether the Reflectix was cold or hot.