My advice, avoid Galleons altogether. Skull and Bones does work nicely on Brigs. It's...how do I describe this...a slightly less "jack of all trades" upgrade than fortune hunter. You lose out on a little bit of speed for more armor and significantly more firepower. I consider cargo space to be a niche stat. It's only useful in one area of the game, and even then it's only a minor quality of life type of buff.