Its not necessarily a bad idea, you just have to make sure its firmly tacked down. If your UTH is already installed you can attach the probe to the bottom of the UTH, you can also put it inside but you need to make sure the wire is completely fixed and not floating around, otherwise there is the posiblity to have your snake get tangled or pull the probe away from the heat source causing the temps to go up. If you do choose to attach it inside the glass and you use silicone, hot glue, or some type of epoxy make sure you don't cover the actual probe. I have hooked up enclosures both ways to see if there was any difference in accuracy and it is about the same, once you get your mat dialed i you are good to go.