After one use, I highly recommend getting some Bondic liquid plastic glue. It's a bit pricey, but I can see it will be very useful. I attached this fin in about 15 seconds. But that took an extra pair of hands. Still, this would have been very difficult even with CA.
I first laid on a thin bead and carefully positioned the fin. My wife then irradiated it with the included UV LED source for about 4 seconds. It seemed sturdy enough but I added a thin layer on each side. I bet this joint is at least as strong as the other three.