Re: Storage of firearms on board
As far as I know, once you are outside of 12 miles (in US waters) there are no rules in particular: I am a Merchant officer and I carry two sidearms and ammunition in a safe in my cabin, issued to me as Master and which I have to declare when I make a port outside of the US.
FYI: the coasties are mostly really good guys and I treat a boarding by them the same way I treat a routine traffic stop. ie., if I am stopped by a cop on the street, I always tell him if I have a firearm and where it is (I live in Florida so check your local laws) and it makes them relax and everybody feels a lot better. I treat the CG the same way except that I offer them coffee; the blueberries aren't your enemy.