How exactly are your shore power cords set up? In post #3 you say you have 50 amp but have 2 cords. That does not compute.
Since you have 240 and 120 VAC in your panel, I would guess you have a single 120/240v 50 amp cord. I can not think of a work-around to solve all of the 240V loads, especially since both battery chargers are 240V.[/QUOTE
His boat comes with a reverse "Y" adaptor (twin 30 to one 50)
Please see section 4-10 of the manual for his boat that he linked in post #17.