Justin,
I just went back and reread the thread. What I didn't read was a systematic look at the AC loads. When the boat is back in the water try this:
Turn all AC loads off including the main breaker.
Turn the main breaker on with all loads off. Does it trip?
Turn 1 breaker on, does it trip? Turn that breaker off.
Turn the next breaker on. Does it trip? Turn that breaker off.
Repeat as necessary.
If a particular breaker trips, that is where the problem lies. If they all work, then it is a combination of breakers that is causing the problem. Systematically repeat the above process for each combination. (hopefully you only have a few circuits.)
Since the problem seems to be intermittent, what AC loads do you have that are intermittent?
The first one to look at would be the hot water tank, if you have one. The heating element creates an intermittent load and is an electrode in a can of water, good place for a ground fault and it is probably empty now that the boat is on the hard.
Next choice would be refrigeration or AC. Refrigeration is probably DC, however, when it comes on while the boat is on the hard, battery voltage will drop and the charger should come on. If it trips, then the charger would be the source of the ground fault.
Good luck.