As part of my original sketch for Ratty, I included a little fender cap thingy on the back fender. I made this today, and actually got it installed.
Flat sheet of thin aluminum, I gave it a quick wet sanding with 500 grit to give it a bit of tooth and wear:
Drilling holes in the back fender:
Fender cap formed into basic shape, with 1/2" speed holes:
Mounted on the fender with rivets:
side view, fender cap mounted on fender: