Pretty cool. I did a similar job on my nylon briefcase. It has a slot in the back containing a 1/4 inch thick dense foam pad. I put a piece of 1/8 inch thick acrylic in that slot. The acrylic panel has holes for screws that thread into Arkel panier hardware.

I think your work looks better than mine because of the foot piece that keeps the bag from swaying. I wrap a bungee cord around my briefcase to accomplish that. The Ortlieb HW is easier that way for this sort of DIY project. The Arkel HW has a elastic corded hook to check the swaying. I stopped short of inventing a way to attach the hook low on the bag.