Coming late to this party but I may have something to add. Sailingdog pretty much covered it but I would like to emphasize that the only long-term solution is ventilation. Dehumidifiers are just band-aids that do not really address the problem. If you can find a copy of the now out of print "The Warm Dry Boat", snap it up. It has all the answers.
In a nutshell, you have to bring fresh air in, through and out of the boat while circulating it through every locker and space in the vessel. The intake vent should be as far as possible from the exhaust vent to allow complete circulation so that water vapor created by cooking, heating and crew respiration, and just high humidity, is carried out of the boat.
We have three passive mushroom intake vents aft, two of them just inches from the transom, one passive exhaust vent over the head, one four inch solar exhaust vent in the forward hatch and one four inch 12V, 2 speed exhaust vent right forward at the bow. There are circulating fans in two of the lockers and passive vents all around to allow interior circulation. Air flows into the cockpit lockers, through a vent into the cabin, through the lockers forward into the forward cabin and head, helped through the lockers under the forward bunk with a circulating fan, and is drawn out through the three exhaust vents forward.
We found we had to create an air space under our mattress and settee cushions to prevent them getting soaked and mildewed from condensation in cold weather. We found a product similar to a loose weave 3M scrubbing pad that goes under the cushions to allow air flow.
In cold humid weather we still get a little condensation in the forward cabin at night but it is not much of a problem. I am considering adding another solar vent.
Or just sailing back to Hawaii so we can leave the hatch open
Over the holidays we left our boat for a month with the solar vent in the forward hatch the only active vent, turning off all the circulating fans and the 12V exhaust vent forward. When we returned to the boat she was dry and sweet smelling so I guess we can say this system works for us.
The book I mentioned, if you can find it, gives formulas for how much air flow per crew member and size of boat. It also has a table showing how much water vapor is created by various types of heating and cooking fuels.