Instead of using paper towels, I'd suggest using coco husk. Not only will it insulate to keep the heat in, it keeps humidity in as well. I would also buy some moss and put it into his hide. That way you can just wet the moss without worrying about providing the right humidity for the rest of the tank.
You might want to find a material to insulate the back and the sides of the glass terrarium so that way you retain more heat inside. I'd use that cork board to cover those sides (if that makes sense).
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