I'm planning construction of a rectangular, vertical smoker. Approximate dimensions are 25" x 20" x 48". I'd like to line the inside with some sheet metal, surrounded by hi-temp insulation, and then wood on the outside. Heat will be either electric element or propane, not sure yet. So, what type of metal should I use? Stainless would be great but I'm trying to do this on the cheap... can I just use regular, mild, non-galvanized sheet steel?