At this point, don't worry about sandwiching the probe between probe and glass - there's not enough benefit versus the risk involved. The back side of the heat mat gets warm too, so just secure the probe flat to the back of the heat mat and set the thermostat based on that temp.
As far as the melting concern goes, would you be worried about it being outside on a warm summer day? Because those will be the warmest temperatures the probe will be exposed to when functioning properly. Translation: nothing to worry about.![]()