I did...
A popular choice are small steel gun cabinets that get insulated...
I needed something much larger that could handle multiple actions at one time, so I visited a local commercial restaurant supply place and found a large aluminum, wheeled cabinet. Would have preferred an insulated cabinet, but couldn't find one. I've never seen a standard household size oven that could fit a barreled action vertically, let alone racking horizontally somehow. Mine is about 6 feet and will accommodate the longest barreled actions with 48" of vertical racking height available. Be sure to allow for space for heating element, insulation, interior board (if using) to make sure you have a large enough "finished" space when done.
Here's the main pointer I can provide- buy the PID controller (and timer, if wanted) from Auber Instruments- resist the temptation to buy somewhat cheaper stuff off Ebay that may not be compatible nor have the parameters that you may want/need.
Again, depends on how "sophisticated" you want to make it. It can be as simple as a locker with a hot plate inside and remote oven thermometer...and time it manually.
Mine is fully controlled, temp held within one degree with the timer starting automatically when the oven reaches the temperature setpoint, and turns off automatically when the timer cycle is complete. My big regret is not setting it up for 220v- easy enough to do, just haven't found the time to replace the 1500w, 120v element and re-wire it. It holds the heat/temp fine once there (and it'll still be hot inside the next morning 8 hours later), just takes a long time to get to 325 for Gun Kote. Cerakote requires lower curing temp ("H" series 2 hours at 250 degrees)
Sorry about the huge pics, no time to resize
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