You should be fine. Two sets of laws covering this. One is the whole safe passage
law which basically states if you are travelling between two points where you can legally possess said firearms you can legally transport them. It is best to carry them unloaded and secured.
The other laws which might cover this is a boat is sometimes a home and as such would be covered not as a vehicle but a dwelling.
In reality it all depends on if the LEO who finds it decides to leave you be or be an ass. People are arrested and charged with imaginary crimes quite often, other times the police simply warn a person or just look the other way.
Whether you decide to carry a gun on your boat is your personal decision, do not let others tell you how to run your life. You and you alone should make that choice.
I quite freqently carry a gun on my boat including entry into foreign countries. I also abide by all pertinent laws in doings so.