Make sure he has a secure hot spot (100 degrees in the heat) that he can go in and out of on his own. By secure, have it so he can bask under cover. If you use a spotlight or under ground heat source, pile folded pieces of card board in the hot spot so he can hide in the pile and still elevate his temperature. This will also give him a wide variety of temps to choose from. Make sure he can get away from the high heat as well so you don't have a second group of problems. Make sure he can choose his temperature options and allow him to do what he wants.
Make sure there are no drafts in his cage, particularly cool moist ones.