You REALLY have to be careful with heat, sometimes. It was over 90 degrees one day, and anything made of soft plastic (CP DEII Clone Emperor Palpatine's Sith Lightning,TLC General Grievous) began to warp and droop. Good thing the next day was cold!
As for sunlight, it's best to keep your collection away from it. The paint basic action figures, if in sunlight, will begin to fade, and look somewhat yellowish. So be careful!