I'm also partial to 3M's 4200 (non-permanent) & 5200 (permanent) adhesive sealants. The 5200 also adheres to hypalon extremely well (assuming that the hypalon is properly prepared for a glue). Be sure to wear vinyl gloves when working with 5200, it will stick to your skin for about a week.
If using the Sikaflex, be sure it is from there marine product line (291 or 292) and not just any type of Sikaflex caulking (which may also contain silicone). As with 3M's 4200, the Sikaflex 291 is meant for low strength adhesion, whereas the Sikaflex 292 is meant for high strength (permanent) adhesion.