Try 3M 4200
I rebedded (not replaced) my ports last year and used 3M 4200 which seals nicely without the future removal problems of 5200. A couple of notes. Drill out the holes to use the "through-screw" system with the male and female phillips head screws. You then won't have to worry about stripping threads in fiberglass. After bedding the inside and outside trim rings, be careful when threading the male screw into the female part that you don't get bedding inside the female end. You won't be able to fully tighten the screw if you do because there is so little clearance inside. Also, be sure to have a cleanup solvent (*compatible with the particular plastic of the port*) to clean up excess bedding that gets on the port. Otherwise, you'll be wiping smudges forever.