When I first put mine in a tub, I just used a lamp dimmer (from home depot) with a UTH from Reptile Basics until we were able to get a thermostat (Herpstat ND) for the rack. It worked pretty good. It usually ran at about 50% and kept the tub at perfect temps (our house was kept at about 68-72degrees. If the zoomed doens't work, maybe try picking up a lamp dimmer from a local hardware store, about $10, they work the same as a "reptistat".
It's important that the bottom of the tub doesn't get too high because even with newspaper on the bottom, the snake could easily find a way underneath the substrate and the newspaper- we have one guy who hides under his newspaper :/
good luck![]()