The seam has a 1mm gap for about 8 inches that is leaking water at a good rate under the door. There is more rust and damage than you see I bet. That raised lip is probably got a wad of putty , foil, duct tape, and rust. You can pour all the stuff you want in there and then work like heck scraping it out next year. You will be happier in long run or short float knowing you have welded steel in place. Gluv it and all of that stuff is great but should be used more as a preventative than a repair. Gluv it peels off easily if metal is oily. Later Dave the Wave at Midwest Amphicar. Viva Celina!