I cut the back off a old under counter kitchen oven, too sheet metal and extended the back so I would have 24 inches inside. My main objective was to do home built tools with a durable finish, and "valve covers" for my hot rods. Them Chevy valve covers were just about four inches longer than the oven and really frustrated me. Taking a alternator apart, coating it, just a few jobs and I am paid up on oven time and cost.
After extending the rear of the oven, TO reinsulate, I used Cer-wool fiber, and recently modified it even more, I cut a 12 1/2" hole in the top to set a pressure cooker pot, and attachments for a "real hot air bender". (to come) I then took some light gauge metal left over from a duct install in a buddies mobile home.
(have to get a current picture)
Heat currently is still controlled by the "remote bulb" thermostat most kitchen ovens have, it keeps the temp in a range of 2 degrees or so of setpoint. THE powders I am using, I heat the parts to 400 degrees, pull them out hot, hit them with the powder, it flows out becoming shiny, then I bake it to set the powder to a "hard state" for the normal 10 minutes set time. You can "burn it like cookies" if you over cook it, but if you do not bake it ten minutes to set, it will never achieve the hardness you desire and longevity in use.
For what this oven cost, time to modify, it has paid for itself over and over.. Only takes 28 amps of 220 volts to operate the oven. (normal house range power is a 50 amp service) BUT since this is just a Built in oven, It does not have all that.
My current obsession is with antique Chevy valve covers, I have 4 sets on my bathroom wall Aluminum holes welded up and powdercoated up. (you put a bit of copper under the breather-drilled hole-crack and a klutz welder like me can weld them up) Horrible is they started making them antique script edelbrock valve covers once again.. Well horrible for me, I don't have the only "pretty set anymore"