I've had poor results with hypalon glue. I have had excellent results with 5200. I added a D ring patch that sees a lot of load and still solid after 4 years.
I taped off very generously to keep the mess under control.
FYI, I talked to 3M tech support, he said there would be no problem mixing white and black 5200 to create a custom grey blend to match your hypalon color. Assuming it is grey of course.