Plugging and unplugging the uth is not a good way to control the uth. I'm glad you bought a tstat.

You said your snake was smart and stayed in his hide and not over the uth. Does that mean you only have one hide and its on the cool side?

You need to have at least two hides and one should be over the uth.

Also just a tip. A dimmer can work in a pinch but should not be relied on to run a uth. The problem is they do not respond to the environment so if the room gets really warm the dimmer does not adjust and it with make it to warm for the snake. Or if the room gets cold it will not increase the power and the hotspot will be to cold for the snake. Also if you have fluctuating temps in the room you will find yourself constantly adjusting it.