The Weaver Snap Davit folks sell a good Hypalon adhesive
. Take a look here: Weaver Industries, Inc.: Adhesives
It is used to attach their davit lifting points to inflatables. You want to use a two part contact adhesive. I don't think UV could have caused your problem. The adhesive is shielded from the UV by the thick rubrail
. It seems that the glue on all inflatables fails sometime. I have a twenty year old Avon
that is in good shape but the glue is starting to show signs of failure. I'll get a few more years out of it with Weaver's glue.