My '95 H23.5 had the same Hella cabin lights as Doug J. Looking up, CW for on, CCW off, push up hard and go CCW some more to get the lens off. They were a real PITA, dim, power hogs and even worse, they frequently required some wiggling to get them to stay on without flickering. (OBTW, the boat was 100% freshwater up to that time, August 2015). I tried some LED festoons but still had the flickering/won't make contact problems. I tried contact cleaner(s), then gentle burnish contacts with thin cardboard, then scrape to bare metal and put a little electrical grease, etc. etc., but they simply would not turn on reliably.
This had been tolerable for overnighters, but I was prepping the boat for a 6-day trip, so I bought four of these Sea-Dog LED dome lights:
https://www.jamestowndistributors.com/userportal/show_product.do?pid=327623
They were a minor pain to install but they fit in the three forward locations. I had to drill holes and the electrical connection was a pigtail, so I cut off the factory female spades and used waterproof/heat-shrink crimp connectors for that. Well worth it though - they were absolutely fabulous after those annoying Hellas. However, they were too big to fit the one aft location under the passageway/above the double berth. I got one of these to fit there, though:
https://www.defender.com/product.jsp?id=1340812
Never got a chance to install it, though. Still have the flickering Hella with LED festoons in it back there.
Long story short, in September 2015 the boat spent 24 hours anchored, unoccupied, about 2 miles off shore in Pamlico Sound in a 3-5' blow. The cabin was mostly dry but full of salt air when we loaded it on the trailer and drove home. It has been on the trailer, wrapped in heavy vinyl canvases, since then. Today I hooked up a test battery and exercised all the cabin lights - and the Sea-Dog LEDs worked flawlessly. The Hella came on after a little wiggle.