Should this be stainless steel or will galvanized steel be adequate. It will be a ring that is 6" inner diameter (slightly larger than the flex liner) and about 9" outer diameter (slightly larger than the damper opening). Seems to me it could get quite hot as it will be making direct contact with the ss liner only several inches away from where it exits the appliance. What type of sheetmetal are prefab fireboxes typically made of?