Someone here, I think, mentioned a Givi tank bag. If I could do it over again I might go that route. If you mount the tank ring to the rack you'd have a quick release for the tail bag.
The design of the stock rack sucks because of the way the slots taper. When you try to lash something to it the straps can move which then creates slack. I strapped a bag of tools in a canvas bag to the bag and at the end of The Tail of The Dragon found that the bag slipped off (remained attached to the back rest) and was rubbing the rear wheel the entire ride- lucky it didn't go lower and lock the wheel. Another time before that, same bag, I had my wallet and other things in that bag and it went missing on a long ride. Long story short, I found it 10miles from home in a ditch- very lucky (again). Be careful how you attach straps to that rack.