I just figured that it is easy enough to just get a 3 bank so when the boat is not in use I can keep all 3 batteries charged. I have not bough a charger yet, maybe I will give it some more thought.
Edit: After thinking this over, with the size, weight, and heat output of the charger (as well as the cost) I think it makes sense to just
buy a 2 bank charger, I have a smaller charger i can use on the starting battery when the boat is sitting at home. Forgive me, for i am a retired engineer and I have to obsess over everything...