Minecarts allow you to place a Chest in them, so... :
Theoretically you should be able to create a larger boat than the vanilla boat that has space in the back for placing down a block while you stand near the front/middle. You could allow the placement of any generator right there in the boat. I'm not sure if this would be easier than the earlier post about placing the generator into the boat's GUI or not. Pick whichever is easier.
I suppose if you wanted to go nuts you could go with the GUI method and make the entire boat modular. You could have lots of optional slots. You could have two slots for engines. Two would increase speed but at a cost of increased energy consumption. You could have a slot for a BatBox. Maybe a couple of generator slots so you could use a regular Generator and a Solar Generator or two Solar Generators, or whatever combo you wanted. Allow the placement of a Chest. Maybe have both Propeller and Jet (the kind that suck in water from the front of the boat and shoot it out the back) engines. The latter might require the addition of a Pump in an otherwise vacant Pump slot. A two Solar Gen configuration might provide enough power for one Prop engine, but not enough for two, and not enough for one Jet engine. However, the BatBox adds some flexibility to that. Anyway, just a brainstorm there. I'm not asking for all that, just putting it out there.