Seam sealer might work, but you should derust the whole flange first. Sandwiches with rust inside isn't a great idea.
I'd offer to weld them up for you, but I'm a long way from you.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.