"My only real concern in your post is you did not mention how you are regulating your heat mat."

It's not regulated, just always on. It covers about 1/10 of the floor area. The floor on the opposite side of the enclosure is quite cool. We thought he'd decide where he wants to hang out... In the winter he spends most of his time over the heater, and recently (before he became totally inactive) he had been going there occasionally but mostly staying in the hide that's away from the heater.