You can specify requirements for a thin flexible heater (dimensions, power, material, leads etc.) here: https://farnam-custom.com/custom/flexible-heaters
The tool allows you to add a thermostat and sensors.
I made my best guess at the dimensions and plugged your temperature numbers into an enclosure heater calculator that outputs a wattage requirement and also suggests a type of enclosure heater. The inputs I selected look like this…
Enclosure is Free-Standing
No Adjacent Objects
Enclosure...