Hi @andycyl -
Cutting the connectors off, passing the cable through an appropriately sized WetLink penetrator, and re-terminating is likely the best bet for a reliable seal. While bulkhead ethernet connector options are out there, in my experience they don’t remain leak tight for very long. The product page has extensive guides to help you select and use this solution.
When it comes to your RTK GPS, we’ve had success simply mounting the antennas under the deck, on the stern and bow side of the starboard/port hull - that makes routing the co-ax into the hull unnecessary! Otherwise, WetLink Penetrators, when used with coax cable, usually need to be drilled out to eliminate the internal step. By drilling the ID out to the OD of the coax cable, you can pass the cable through without having to remove the outer jacket, and re-terminate the connector. This does compromise the depth rating, but only at extreme pressures - your BlueBoat won’t be going below 40-100m!