I have not finished my cabinet off yet but I think I would put a fan in the top of the cabinet and a vent a on the opisit side. You can run a humidastate or just run the fan all the time one can buy small fans at princess auto for next to nothing. Very quiet and removes humidity. This way there will not be any moistur build up or corrosion. Some times its the simplest things that are the answer to the problem. resposible manufatures with high end cabinets do this for you or they use to.

Bill