I am considering making a wooden cage for my BP. Since a UTH or Flexwatt won't heat from under a piece of wood, I'd have to place the UTH or Flexwatt in the tank itself. I'll then put a piece of glass or plexi glass over top of that. Now my question, which I have a good idea of the answer, but want to have it confirmed, as long as the UTH or Flexwatt is controlled by a thermostat or rheostat, it won't crack the glass, right?

Also if anyone has any experience in making their own cages, will the polyurethane sealant last a bp's lifetime?