Once back when I used tanks my normal pushed away his substrate(as almost all BPs do) and curled up right over the glass on top of his UTH. When I picked him up his belly was very red and 3 large blisters had formed where his skin contacted the glass. What I had to do was go out to walmart and get a dimmer switch and a 6ft extension cord. Cut the extension cord and ran it through the dimmer switch and made myself a sweet rheostat.
However as the temperature in the room change the rheostat had to be changed also. Eventually I just said screw it and moved to a rack system with Helix thermostats which has been great.