The 16 gauge aluminum would work very well, judging by the time I covered the KP top grill with foil. It worked great, with the kettle running somewhere north of 900...until about the fifth pizza when the foil burned up and started falling into the pizza. Aluminum thick enough to not be damaged by the wood fire would do the job. I think that the trick is to reduce headspace.
I have the Baking Steel, the regular one, not the one above. Now I just set it on the top grate and it works pretty well.