I decided to use the "40 year rule" on this portion of my project. If it lasted for the last forty years at age 58 why should I worry about it lasting longer than that!
Therefore, I fabricated an aluminum 1-1/2" x 2" angle (106/74 deg.) out of .100" aluminum and installed it like the original.
(BTW - I know that I have still not removed that trailer bracket from the bumper - but I will when I find one of those round-to-its!)
When I first reworked my frame I added a couple of angle iron clips to the outside of the frame.
With that additional support and with the addition of this flashing
that I had previously fabricated and a little bit of Vulkem I think it might last long enough for me.
It's time to move on to bigger and better things.