There are some weather proof receptacles and matching plugs. The type that would meet my criteria for use would be a 15 or 20 amp 120 volt twist lock female receptacle and locking cover similar to the 120 volt 30 amp male that you now have for shore power. It is absolutely necessary to have ground fault protection for that plug. Hubble has some ideas, personally I run a cord from below but I'm lazy and cheap. Fair winds. http://www.hubbell-wiring.com/marine/pdf/twistlock.pdf