When talking about stainless steel, it's important to remember that stainless has a much lower heat transfer capacity than mild steel, and only about 15% of the conductance or transfer capacity of copper. While some of that might be mitigated by a thinner skin, at least than mild steel, and bring the system closer to an equivalence with mild steel, I don't see you gaining much, in either the short or the long run, by making that compromise