For anyone else that sees this and plans to build it.
If you remove the thermostats, usually there are 2 of them, from an old hot water heater and install one in the middle of the box. Connect it in series with your light and it will allow you to set the temperature inside the heater to the exact temperature that you want it.
I have mine set to 104 F.
You do not even need the dimmer. With the thermostat, the dimmer just allows you to control how fast it comes up to temperature.
Jim