If you are just plugging leaks you can solder or braze the holes. Make a dimple at the hole, use a lot of flux if soldering. Silver solders of varying content are wonderful. If you have a broad rusted area solder or braze a patch on it and then french it in with bondo for looks. Use Muriatic acid to reveal all your leaks. There is a pouch like structure in the lowest part of the tank in the frame that often has leaks so check that good