Thanks! I'm using repitbark as my substrate. I have one larger UTH under my warm hide and one smaller UTH under my cool hide. Both are regulated by a thermostat. I'm using a digital thermometer and hygometer (sp?) by Zilla. I put the probes about halfway down the back wall in the middle of the tank. I have backing on that the probes are behind. There's a cut out in the backing to allow for probes, wires, etc. The backing is a styrofoam like product, I forget who makes it.