The Zilla control is a tstat guys. Its the one the big pet stores carry.

OP,

You do need a tstat on a uth. The best place to mount the probe is between the uth and the bottom of your tank. You may have an issue with the tank not addition level because the temp probe for that tstat is huge. Do the best you can and gently peel the uth back until you can place theprobe on it. Then you will want to add some foil tape or duct tape to it to make sure it does not fall off. If I was you I would set up the tstat you have (unless it can be returned) but order another one. The Zilla is not digital and dialing it in is not as easy. They also do not have a good reputation for lasting. I would replace it soon and just keep it as an backup/extra.

The substrate over the uth needs to be shallow so the heat can pass through and be utilized by your snake. You only need about 1/4 inch over it and this is the reason you need a tstat. An unregulated tstat can get very hot and with the shallow substrate can harm your snake.

As for the hides being to big I like to put moss inside them to make them seem smaller. This also becomes handy during a shed. You can mist the moss and it turns your hides into humid hides.