steel bell for batch box heater

I'm rebuilding my sauna heater. I'll use refractory parts for the combustion components, but I want to build a good-sized bell out of steel. the sauna doesn't need to stay hot when it isn't in use, so extra mass would be a liability. steel should heat up much faster than more traditional bell materials.

my question is what gauge steel should I use? lighter would heat up faster, but I don't want it to be flimsy. it'll have maybe 75-100 lbs of rocks on the top. my first thought was 16ga, but I don't know much about these things. I attached a draft line drawing I'm working on.

also, if there's any reason this is just an entirely rotten idea, I would like to know now before I get too far along. so don't be shy about trying to talk me out of this.

I would guarantee that 16 gauge would be strong enough to hold up without waffling or buckling. 20 gauge would probably be strong enough. It depends in large part on the span between bends - what is the width of your planned bell?

I would recommend galvanized steel for the sides at least, to minimize rusting. High-temperature stove paint might protect plain steel well enough. The top will get hot enough over the riser to burn off galvanizing, so heavy steel or stainless steel would be the way I would go for that.

The speed of heating up is pretty much irrelevant - any sheet metal gauge is going to be hot in minutes. My 1/8" steel access panel in my bell gets warm within a few minutes of starting a fire, and it is mostly below the level of the riser top.

thanks, Glenn. that's good to know.

thinner steel is generally cheaper and easier to bend but obviously not as strong. so if 20ga is fine for heat/buckling purposes, is it enough structurally to hold some weight on top? I suppose I could use some angle internally to stiffen things up if necessary, but I have no idea whether that would be cost effective.