If you have a dremel grind out all the bad rust then coat with lard or bacon grease before sealing with fender washers amd such. I just fixed the same thing on a kettle I flipped.
I was thinking fender washers and a 1/4" stainless bolt. It ain't going to be pretty but I'm not entering in the county fair or anything. As I said, I have other kettles to cook on, I just want to keep this one in the game a while longer.
For aesthetics, if a fender washer will cover the damaged area, then go for it.
If not, then make up your own fender washer from some sheet metal.
You could even make the patch oblong.
That might take two fasteners, 1/4-20 or 12-24 or even 10-24