Mr. SE-R....Its not worth fixing,so you should just sell me the car
Seriously,though that sucks
Especially since it has been out of the sun.
Its not necessarily the sun that makes it warp.Temperature changes can effect it as well,and most of all it just dries out over time.All you can do is treat it with a good quality product that helps keep it moisturized and hope for the best.
as for the heatgun or silicone to hold it ...good luck with that,I have never tried it