On the rear fenders, I ended up fixing them.
Here is result; I cut the HVAC strap and used the rivets as discussed.
Put them on dry. This should ensure the don't flop around and the crack does not propagate further.
.
I then applied the goop to the inside, prior cleaned with rubbing alcohol.
.
.
It dries very quickly, but has some flexibility like the label said.
The goop costed $5 at home depot, I was not sure if it was going to work, I feel it will enhance this fix.
As a back-up I got 1 quart of truck bed coating, seriously I was going to coat the inside and outside, letting it dry, but now i feel no need,
That stuff is $20/quart, I'll be returning it tomorrow.
Will let them fully cure for 48 hours before putting back on.