There's one other thing that you can try. Use bar clamps to close the crack. Drill two 1/4 " holes on the bracket a couple of inches away from the crack. Get some epoxy putty designed for potable water repairs. The stuff you knead together to activate. Push the putty into the two holes to give it something to grab hold of. Apply buttons of epoxy on the underside of the holes. Then apply a thick (maybe 1/4" thick), continuous length of epoxy putty from the holes along the bracket, over the crack, up and over the back of the tank. You are essentially constructing a splint out of epoxy putty.