BEETLE, one down side to doing that is if you are plugged into one shore plug the other will be energized. That presents a dangerous situation. You would have to have a way to disconnect the one not in use. One way would be to add a dryer type plug in the basement. Male end to the wire that feeds the breakers, and a female end on each of the wires coming from the shore plug. So figuring the expense of buying a new Marinco plug, some wire and other stuff, I'm thinking that a new extension cord might be the ticket. I carry a 15 foot 50 amp ext. extension cord. I think I paid around 100 bucks. I have not had a need for more...........yet.
Let us know if you do add another plug, and how you did it.
Peace
Dave