West Marine sells a light bulb type of 'dehumidifier' but I don't know if it will handle heavy condensation. I think it's make for winter storage situations. The problem you have may be due the moisture from the living, breathing humans living aboard. With every breath you take you pump warm moist air into the boat -- it cools and sinks, contacts the cold hull / sole... et voila! A cabin heater might help. If you have shore power you could find an electric model, or if you're on a hook you might have to install a propane or diesel heater. If you go with a diesel/propane heater, make sure you buy and install properly a carbon monoxide sensor/alarm.
Also, seek professional advice on installation of a fuel based heater, fuel storage tank and supply lines. I have a friend that lost his boat in a fire that errupted during refueling of the diesel heater. He escaped unharmed, but the boat was a total loss.