That's not such a dumb question, Mr Stringmaker. In fact, as I think I mentioned in my earlier post, I even tried a batch using the steel lid from a US Army WWII mountain cook kit. If one is going to make this as a trail bread, you're probably not going to have a heavy cast iron skillet along anyway. I also mentioned somewhere that I had been looking around for an old-fashioned steel skillet for an old time feel. I have seen a couple but didn't make the plunge. Something like that might be a little more suitable for trail use.
Anyhow, when using a thinner skillet, you should need less heat but you'll have to try it a few times to get the hang of it. As for making a thinner bannock, that's not something I've tried. Either way, the size of the skillet doesn't matter; it's how thick it is. I've seen one steel skillet that must be close to 14 or 15 inches in diameter with a handle that was about two feet long. Believe it or not, it was for sale in an L.L. Bean store. It was clearly meant for campfire use.
While I said it doesn't matter how big the skillet is, it still has to be big enough or you'll have to settle for a really small bannock and that probably wouldn't be worth the trouble. The old Boy Scout mess kit/cooking outfit, which may or may not have ever been used in the U.K. comes with a small pot of maybe a little over a pint, a deep plate (about the size of a soup plate) and a skillet with a folding handle, as well as a small cup. For one person it isn't bad but the whole thing is made of aluminium, so the skillet doesn't lend itself to slow cooking. And for something like a bannock, it's really too small since it can't be any bigger than the bottom because you have to turn it over. It's worth trying though and maybe I will this weekend, if the spirit moves me. I suppose you could use any flat metal surface like a cookie sheet, a proper griddle, the mudguard of a tank, things like that. I suppose if one were willing to try something really primitive, you could try it on a flat stone, if you happen to live where flat stones are common.
Some older books on the subject, and here I'm probably remembering W. Ben Hunt's well illustrated books, show bread baked before a fire by being wrapped around a stick. Now that would be a challenge and it might not be bannock.