I am with you Mike, flanges and backing or butt are all options and they all can be the perfect way to do a particular splice.
I have pointed out before but every single body is held together with lap and pinch welds. There are hundreds of these welds on every single body so as far as rust and moisture collectors, the entire body is held together with them before you even start. So I don't worry about that, simply seal it properly and you have at least as good as the rest of the body.
It is true that many manufacturers guidelines are now eliminating backing and going to butt welds.
As a balance between what is the "bestest" way being with skills, with expectations on that particular job, etc. A butt weld with backing or butt weld or flange weld could be the "perfect" way to do it.