I used powder coating on many items as a HD mechanic .. Engine parts never melted or failed..
Cylinders, heads, rocker boxes, engine cases and side covers got very hot..
I even had a high temp flat black on a stainless exhaust that worked perfectly..
I was great friends with the powder coating guys in Atlanta..
They started out doing this for their own hot rod restorations and it evolved into a huge, successful business.
I worked on Terry bikes at my home shop and he always took great care of my powder coating..
I built two bikes that were completely powder coated..they are more than 10 years old and the powder is still perfect..
Applied correctly you should have no problems with a powder coated smoker..
The only issue would be cost..it is expensive....
Here's my buddies web site..
http://www.headercoatings.com/
Craig