The probe for the thermoSTAT should be taped (foil tape) to the UTH OUTside the tank. The probe for the thermoMETER should be INside the tank right over the UTH under the substrate. Best ways to attach are velcro or hot glue.

Oh, and make sure your tank is covered and insulated on back and both sides for heat regulation and security (of the snake) and that your screen top is covered with either the foil treatment or plexi for humidity retention.