Start first with not installing it unless you have a thermostat to regulate it.
AFTER you have a thermostat you can then install the UTH outside the enclosure under the hot side hide.
The thermostat probe will go between the mat and the bottom of the enclosure.
The UTH plugs into the thermostat and the thermostat plugs into the wall.
Adjust your thermostat to no more than 95 degrees on the inside surface above the mat.