Putting the 4" port behind the rear beam sounds like the thing to do if you can do the repair with that access. It's a pretty standard spot to have a port, I've considered putting a port there without needing a repair just to make it easier to clean water and debris from near the rear drain.
I don't think you will find anything in your way, but let us know if you do!
Please take pictures as you do the repair and add a folder to the "Beachcats Technical" section of the photo albums so others can benifit from your experience.
Good Luck!
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Damon Linkous
1992 Hobie 18
Memphis, TN
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