It doesn't exactly spray. Don't want to seem like a know it all but my dad was in on the beginning of the powdercoat process. He ran a wheel company. They bought one of the first powder coat lines sold. Ithe clean piece is electracally (?) charged and so is the powder. A low pressure air or kinda "poof" is blown on the part and it is drawn to the part. Then it is put in the oven. Process is great. 400 is the minimum temp to start process. About the only way I had ever seen him get it off or strip it is with extreme temps. Great coating.
You are correct. I run a powder coat paint booth were I work, we only use gloss black but there are all kinds of colors and all kinds of finishes. We use to use a hybrid powder paint that required a 425 degree cure for about 30 minutes but now for conservation of propane we use a standard powder coat that only requires 320 degree cure and as little as 15 minutes cure time.
Not being an electrician or tech I don't know how you would achieve the required charge to make the powder stick I do know that it is an extremely low charge something I think you would only need a flashlight battery set up to make work for short durations.
Low air pressure is inportant because to much pressure will just blow the powder off and away from the part causing thin layers and holladays in the finish. The part must be free of any grease or lubercant or the powder will not stick and slide down the part like a run with conventional paint when it is cured. It will look fine when you put a coat on but will show up after it is cured. You can just grind off any paint defects and spry that area again.
If we have a bad powder coat job which happens daily we have an oven that burns the powder coat off at 1400 degrees for 5 hours. It does not have to be that hot but we make radiators and they of course have hundreds sometimes thousands of nooks and crannies and this heat will reach all the inside painted areas. Powder coating should stand up to the heat of a uds with no problem but they do also make a high heat coating. Please don't paint the inside of your uds.
The only problem I can see with powder coating a uds is the uniformity of heat distribution during a cure process, if you were to build a fire inside the barrel being much hotter at the top then around the bottom especially under the fire livel. Maybe setting the uds up on a fire grate of some sort and building a fire with charcoal not wood, being carful not to let flames lick aroud the ouside schorching the paint. Leave the lid on to keep heat in and curing the lid in the process. I don't know just thinking out load here.
A person may want to try to locate a powder coating shop around there location, it may be worth while even if you have to spend a little. The major expense would be in prep and set up, it takes very little paint but by the time you buy the spraying unit the paint and figure out how to cure it, prep the uds, ie., taping off any threaded parts, holes and any areas you may not want painted, well you get the idea. I would also think it would be just about as cheap to do a couple drums at the same time, if going to a shop.