Don't forget to paint with that rust stabelizing paint, you know, it is milky white, dries black on rust? It looks as if there was considerable acid oxidation more than ordinary rust there, so some acid resistant final coat, or that spray undercoat/bed liner stuff.....Looks as if a single piece of steel might do it, with 3 bends in it. Also, there are flange creating vice grip pliers, so you can make a flange on your patch and rivet thru it . Works easiy.