My surface temps are 90 and 80 hot/cool with an ambient of about 82. I use paper towels as my substrate too. I'm also using a rack system with 3 inch tape controlled by a helix proportional thermostat. I don't believe the part of the tub that touches my snake ever exceeds 95 degrees; with my substrate temps never going past 92.

I would venture to guess that your ambient room temps are too cold. I had to insulate the exposed portions of my tubs in my rack in order to correct my issues I had with my thermostat settings.

Anyone else want to chime in?