3M 5200 will definately seal your port, but it will be forever. 3M 4200 does not have as tight a grip and will seal just as well. Silicon will probably need replacement after a few years (yes even the 50 year stuff). Epoxy is another permanet fix. Last year, I was up grading my Fish and sailing in between upgrades (one thing at a time) and used plumbers putty to seat my ports. I did this inorder to remove the mounting flange for more room in bolting down the the main halyard pully and cleat and fixing the new rudder mount. Every thing remained tight and was easy to remove each time until I completed the upgrades. I have since used 3M 4200 to seat the ports.
What if you'd ever lose the port covers and couldn't find exact replacements? I've also had sand unbeknownst get in the threads and make them rough and difficult to remove... might need replacing sometime. Also, mine are getting faded and not too purty... might replace with newer ones. FWIW, I'd reconsider 4200.
I was considering putting an inspection port in the foward bulkhead of my cockpit as opposed to havinging it visible behind the splash guard. I know I still could reach the forward fittings, but would have a harder time reaching the halyard cleat and bullseye.
I want to beable to mount the hiking strap anchor point as of now. Everything else seem fine.
Putting an inspection port in the foreward bulkhead is defintely the way to go -especially if you are under 21. With a port there you can hide a 6-pack of beer inside the hull and then when there's a delay in the regatta because of no wind you can get your head down in the cockpit and guzzle your stash of beer without the RC seeing you. Just remember to share the beer with the old geezer that gave you this tip.
I would not put a port in the front cockpit wall like you are contemplating. I would place a 6" port behind the splash rail. In this position, 3" from flange to rail (both sides), the center of the port to the lip of the cockpit is 18", give or take an inch or two. You will have to reach around the dagger board trunk to install your hiking strap, no big deal. With a port behind the splash rail, you can reach/repair the dagger board trunk, mast step, cleat, and halyard bullseye or pulley. If the port was in the front wall, you could only reach the dagger board. If some happened to the mast step, you would have to put the port in anyhow. The SF bible (pg 249) has a picture with two ports in the front wall, the text says this is an idea location. Maybe so in 1984 when Derrick Fries wrote the article. Current thinking is behind the spash rail and by the rudder. Check Wind Line Sails (www.windline.net) and Mike Kilpatrick (http://mikekilpatrick.homestead.com/) to see how they position the ports they install. Good Luck
I set my first port in silicone aquarium sealer. It worked great.
Years later I decided I wanted a port with a dry bag liner. I removed the screws, worked a putty knife under the lip and the ring peeled up with only a little effort. The bulk of the sealer peeled off the deck after I loosened one spot with a single edged razor blade. Rubbing with a dry rag peeled up the residule bits.
The new port with liner was set in marine silicone calk (probably GE). It's holding solid and dry after 10+ years. On the other hand, the port's O-Ring has needed replacing twice in that time period. Marine silicone calk is my sealer of choice these days....