I have been running my UTH since mid October and I am never worried about it because I have a proper thermostat on there. If possible, I suggest you pick up a Herpstat or a Vivarium Electronics thermostat, they will give you a lot more peace of mind than a rheostat.
Also, if you dont have one already, get a dimmer for your heat lamp and use a infrared bulb so that you can run it all night if needed without your snake freaking out. I use the heat lamp cranked extremely low on the dimmer to control my ambient temps and I never turn it off (it keeps the cool side ambient at about 78-80 at all times, and the warm side ambient between 81-83). The heat lamp does kill humidity, so I need to mist about once or twice a week, and once or twice a day during shed. Choosing the right substrate can also influence your humidity levels.
You can also try to cover the screen top with aluminum foil, that helps with humidity. Just leave a 1" inch gap at the back and a spot for your heat lamp.