Youre actually going to want to move the thermostat probe OUTSIDE the enclosure. Being inside it can be peed on, water spilled on, laid on, etc....which can all cause inaccurate readings which could result in dangerous heat spikes.
You also want to check the actual surface temp, not the substrate temp. Your snake can and will burrow and/or push substrate around and end up lying directly on the enclosure floor. Most of mine push all the substrate out of their hides anyway.