What I did on for my knees was gorilla glue the inside end of the elastic strap to the inside knee wing. That means for the left knee you would glue it to the inside of the right wing, and on the right knee you'd glue it to the inside of the left wing.
As for snaps, I put 2 male snaps on the outside wing of my knees...about half an inch apart. This way if one comes off while trooping, you have a back-up you can use. You only need 1 female snap on the outside end of the elastic strap.