Eric;

Galvanized steel is very popular too. It's cheaper and certainly easier to work with then stainless steel, and if you screw it up, you’re not out much money (most folks have to special order large stainless sheets). Also, keep in mind the word "stainless" actually describes a large array of types. All the way from Chromium /steel (like used on steak knives) to Nickel/steel (like used on pots and pans) , and about 100 types in-between. When you order Galvanized steel, it’s all mild steel, with only about 1-2% carbon, is easy to drill, cut and bend, but can take the heat of a fire (it’s not as pretty though as polished stainless !!! ).

I personally use stainless pop rivets though, instead of aluminum on the firewall. They hold up better to heat in the event of a fire (look for the high sheer strength type, like kitfox provides). You will have to special order them, to get the good stuff.

Hope this helps

Roger