Brian Atkins, Atkins & Hoyle Ltd. We are Marine Hatch
and Port Manufacturers.
There are a few makers of hatches
and ports left in the world today, several mentioned in this post will 'get the job done'. From our experience, plastic ports just don't seem to last as long as metal ones. We have also found that extruded hatches
and ports tend to be much weaker then cast, and are not as easy to repair
when the time comes due. On many boats, especially those in salt water, lower quality metal hatches
and ports will rust over time.
In terms of sealing around the frame of your hatches or ports, we recommend Silicone as well. We used to use Butyl Tape, but it can be very messy, and doesn't seem to provide as good of a seal. Often just a small bead of Silicone around the edge of the frame, and a little around each screw hole, will work great as a sealant. Fresh Silicone often 'squeezes' out once you start tightening the frame to the boat, we often recommend taping off around the frame, and allow the glue to 'tack' up before trying to clean up - otherwise you may just spread wet silicone everywhere else.
There are stronger adhesives available, but we find the silicone seal lasts for more then 20 years before needing to be re-sealed. This is often perfect timing to have them re-furbished and put back on the boat with new sealant.
If you are still having issues finding something of high quality and that fits into your pre-existing cutout, feel free to PM me and I will help direct you as best we can. Thanks.