One thing I learned with rust is that rust is normally more than what you can "see." Once you start grinding and cleaning up the area, you have to be vigilant that you are really getting all of it. Sometimes a tiny spot is just the tip of the iceberg and it will grow a lot until you hit "good" metal. Paper thin or the zillion tiny holes must go before you can weld in a patch panel. Not trying to jinx you or "scare you" just things I have learned along the way. BTW -- make sure you check under the battery tray.