I only use my top twice a year. Once to put it down in the Spring and once to put it up in the Fall. Really don't know if it is a humidity or UV or heat or combination of all three. Maybe usage has something to do with it also. I notice when I drive to Phoenix nobody who has a convertable has the top down in the summer. Tops down seems to be reserved for Fall, Winter and early Spring. In Arizona those that keep their tops up have problems with UV rather then humidity but heat could be an issue at 120 degrees. My summers are about 75 to 85 but then again I live in the mountains of Arizona at 7000 MSL. I have never seen any correlation between these factors to determine why the problems are happening with the back window falling out.

Are you refering to the back window problem or the tearing or both? Based on other posts from Europe it appears that the rip is a mechanical defect not an environmentally caused issue.