When I mount probes of some sort to the inside of a tank i either use suction cups and pull out the little hook from the cup and feed the probe and wire through the hole that the hook was in, then stick it to the tank. If the probe is to big to fit in the hole you can use sewing string feed it through hole and tie it to the wire or probe and cut the excess string to where all is left is the knot. That way if the critter gets behind the wire somehow, the suction cups will pop off the tank side and not trap itself. Just make sure you take the excess wire out of the tank to prevent entanglement of your snake.

My other way is using styrofoam backgrounds (non toxic) or styrofoam you can find within appliance boxes and clean them. drill/cut a hole through the styrofoam just big enough for the probe to fit through and have the wire behind the foam. The downside is that they tend to mildew and deteriorate (you can youtube it to make it last), and takes up space within the enclosure (KEEP HEAT SOURCE AWAY). On a good note styrofoam provides decent insulation.

Under no circumstance use tape on the inside of the enclosure, its a disaster waiting to happen.