For a long time I have struggled to get my E-Tex and paint just the right temperature ,due to my basement is to cold around 68 degrees I had an electrical control metal cabinet in my shop that was just right for my project, box dim.3feet x 2 feet x 6 inches deep. You can make this box out of just about any material including some kind of fiber board. I insulated the entire box with one inch insulation from Home Depot. The box can be any size.
Make sure that you put a divider in the box so you can install a very small 110 volt fan to circulate the air when the stat calls for heat by using a light bulb any were from 40 watts to 100 watts. Note the fan only comes on when the bulb comes on, no need to run constant. I set the temperature control to come on at 74 degrees and off at 75, works great, no more warming up anything
I have made a simple wiring diagram, make sure is fused 5 amps plenty sufficient to run the fan and light bulb
The A419 Johnson control you can purchase at any heating and cooling suppliers, the 4 inch fan 110 volts got it at Scientific Lab supplier the rest at Home Depot
Here some pic