I've been looking at http://www.creationkit.com/AddHavokBallAndSocketConstraint_-_Game to try and attach objects together, but either it doesn't work or else I just don't know how to use it. Also took a look at http://www.creationkit.com/TetherToHorse_-_ObjectReference but I think it only works between carts and horses.

For actors, you can use http://www.creationkit.com/SetVehicle_-_Actor to attach them to the 'Ref_Attach_Node' on the boat. Then you can have them play an animation to move them around, like when you start out on the prisoner cart in the beginning of the game.

That would be nice anyone has an idea of how to implement?