Ug, I can't stress this enough. It is so annoying carrying a cart full of stuff, then you hit a river. So I say you should be able to put a cart in your boat. I know it seems illogical, as the cart is bigger than the boat, but it could take both spaces. It would be a whole lot easier than moving all your stuff across a river or something then making another. Unless there is, of course another way I don't know.
Discuss.