When the inspection port gaskets were cured I undercoated and painted the edges on the outer circumference where they show in the cabin.
Then I dry fitted them all by marking out and drilling pilot holes for the fastenings, and screwing them into place.
Here is the starboard centre board case port.
I even dry fitted the drain bung ...
Finally I fitted the inspection port flanges, using white marine silicone rubber caulk. The brand I am using is Geocel, supplied by a local chandler. They say it is manufactured by Dow Corning, which comes highly recommended on many boatbuilding blogs, so I guess it's fine! It works nicely, doesn't go off too quickly, and is easily cleaned up with methylated spirits while still wet.
This is it.
Here are the centre board case flanges sealed in place.
And here is the bow compartment flange sealed in place.