Step Three: Bottom Brace
I drilled out holes in the main brace and the ammo can and bolted the cans on behind some rubber washers.
I used a 3/4" two-part locking collar
to grab around the rear fender bracket.
I welded 1/2" steel rod to another piece of angle iron. It was a tedious process of setting the unfinished bottom brace into place to get the stand-off distance just right.
Place, grind down, replace, grind down some more. Wash, rinse, repeat.
Once I had the stand-off distance right, I tack-welded the rod to the locking collar while it was on the bike, before removing it to get a better weld.
That gives each can three points of attachment.