I just have a regular big dry bag and attach it, and other loads, by running a cinch strap under the pillion seat (slide under just past the rubber bumpers) along with a climbing runner (red) that runs under the bracket and has carabiners on each end.
This allows me to strap the load from left to right from under the seat and fore to aft using the two biners and the backrest or luggage rack as attachment points in the rear.
I'd say this weekend, but watching the Tyson fight and, for different reasons than Jake Paul, I'll probably be no good for getting out and about for a couple of days afterwards.
Sorry, I don't have any photos. I've only actually used the US30 once, but it worked great, was very secure and very comfortable to lean back against on a long ride. the 2 forward straps went around the frame under the seat (and came around the outside of the seat) and the 2 rear straps I secured to the metal base that holds the back support.