These have kind of chunky probes. The heat mat UTHs you generally get at pet stores are mats with adhesive. It sometimes tends to bump the UTH so there is a gap if you try and stick the probe between the glass and UTH. The solution is to get styrofoam board and put that under the entire bottom of the tank. You then can stick the UTH to the bottom of the tank and stick the probe on the UTH and use the styrofoam to hold it in place. You can also put a strip of duct or alminum tape ont eh probe cord close to the probe tip but not on the tip and tape it to the UTH.

So it would go from bottum up: Styrofoam > probe > UTH > tank.

This works just fine so long as the probe tip is in contact with the UTH. Place it so it is roughly centered on the mat. Again the styrofoam will keep it all in place because the weight of the tank will keep everything from moving around.

I do this on my Rosy boa tank and it works perfect. There is nothing wrong with those zoomed under tank heat mats. They have been used for years and years and are UL listed. They simply need to be regulated down with a thermostat.