I would encourage anybody who wants to understand this problem in more depth to read this excellent blog post:
https://wp.me/p30LrV-wT
Although most of the points have been covered in this thread, there are several salient points in the post.
Good article to read.
On my own older boat, it has a Square-D panel. I swapped out four 20 amp normal breakers for GFCI-AFCI combo breakers on the hot water heater, Cruisair heat pump-AC, outlet circuits, kitchen circuits (MicroWave but NOT the fridge).
That leaves 3 circuits, the fridge, Princess stove, a forward, and aft electric heater without GFCI-AFCI breaker protection, and one unused circuit left in the panel.
That Square-D panel has twin 30 amp input with separate neutral busses for each incoming hot wire.
Those breakers will trip at 5 milliamps, far below a dockside 30 milliamp breaker. So far only had the outlet GFCI-AFCI breaker trip 3 times in the last few years, and may have happened after heavy rain, otherwise unknown nuisance trip reasons. But might be because too many outlets for that one GFCI-AFCI breaker.
I must have 20 outlets on that one 20 amp circuit running all over the boat. A couple extensions to the circuit to potentially wet areas, I plugged in extension cords running to a couple of fixed outlets, which can be easily unplugged to disconnect them if they get wet and would be continually tripping the gfci breaker.
I used to have a gen 1 galvanic isolator, before I installed the GFCI-AFCI breakers, one day I noticed it had failed. It burned up because a wire got wet in the cruisair connection box that runs the AC water pump, so it leaked enough current to kill it. Happened before I put in the GFCI-AFCI breakers.
TODAY, if a leakage current happened again, it would simply turn off the power to the Cruisair courtesy of the GFCI-AFCI breaker in my Square-D panel.
So very glad I never bought the gen 2 style isolator to replace it.