I built my own curing oven out of chimney flue, available at any hardware store. IIRC, it was 8" inside of 10", seperated by 1" of insulation all the way around. I built a frame to support the flue above a hotplate (cheap, abundant and replaceable). I'll try and post up some pics in the next couple of days.
At the end of the day, if I were only doing small quantities or just one rifle, I'd just send it to a certified applier. Not cheap, but cheaper than building your own in the long run.
Do yourself a favor......DON'T Cerakote the inside of any Action, you'll regret it.