Yeah I usually laminate the frame a few times for strength. I just thought of something you could also maybe use toothpicks to strengthen them.
When I did the grasshopper version, I used a Ziploc sandwich bag for the windows but they are thin. Maybe you could try using one of those freezer bags they're a bit thicker, or use clear packaging tape. Hope these ideas help.
What we obtain too cheap, we esteem too lightly: it is dearness only that gives every thing its value. Thomas Paine, Founding Father