From the research I have done here and elsewhere the UL rating should be UL-103 HT.
Simpson uses a 430 SS inner and outer in their products. UL_ 103
Selkirk/Metalbest uses 304 inner and 430 outer in their products. About 42.00/ft plus your Tee etc. http://www.selkirkcorp.com/WorkArea/sho ... px?id=7468
They also have 316 SS but Europe sales only due their codes. I asked why not here, they replied Canadians and Americans would not pay the price.
That would be the way to go.
Stainless outer only with the coal.