We would like to go farther on a load of ice in the icebox on our '77 h27. Most of the power will come from shore charging of our house battery, since we have a small alternator, and most of our stops on Lake Erie are in marinas with shore power.The ideal set-up would be a 12 volt cold plate that we could retrifit into the box somehow. Then we could run it off the engine while motoring, and through the charger while tied up.Has anyone heard of a cool plate, or other retrofit that would work?DavidLady Lillie