I use small muffin fans. The case size is 90mm. They each draw about 10 watts at 120V. I buy them from Newark Electronics by internet. Almost all are ball bearing, not the sleeve bearing units. I do have some sleeve type but they have given me trouble.
I place several of them around the boat. Actually the last time I counted there were 17 total.
4 in the salon, 4 in the v berth, each set up to force a circular travel of the air.
2 in the head, one pointing in and the other out the propped open door.
The flow is arranged so that circulation goes past the Evas.
1 blows out of the V berth. 2 in the engine compartment, 2 in the lazarette all again circulating the air.
1 pulls air out of the bilge area in the v berth as it is quite enclosed and gets water into it from the chain locker.
This way the odds of localized stagnant, high humidity air is minimized..
2 are mounted in the salon windows, one port, one stbd., so they blow OUTWARDs.
It took me more than one winter to set this all up as some of the fans and placements were reactions to specific problems due to humidity.
The EVAs are on a timer set to run twice daily for ~ 3 hours each time. Not much point at night as they can freeze.
I also use several low wattage heaters each on a T.stat so they only come on when the temp. heads for freezing.
My boat is also under a full custom cover/tent which was made for it so although some rainwater gets in, the boat is protected. Just not perfectly.
Part of the reason for all the fans is when we came home from our winter travels there was a faint dampness odour, sometimes stronger than I liked. I was not happy. With all the fans that odour is gone.
A wet bilge will not help as that water is a source of constant vapour. Either adjust the stuffing box to cut water way down or figure out a way to keep the level way down. I don't recommend cranking on the stuffing box as the next spring at recommissioning time loosening the nuts will NOT loosen the packing and then may be too tight. Just adjust so the absolute, acceptable minimum drips through.
I'm home this year, no travel, but normally what I have done above takes care of things for me. Of course the boat is fully winterized on top of my fancination. I just don't want that odour or the resulting mildew spots.
If you are able to monitor the boat frequently during the winter then a lot of this may not be required. Before we started travelling I would go and open the boat two or three times weekly and work in the cold, letting the breeze blow through. Cannot do that and don't like that so much anymore.
As for the question about the dehumidifiers, YES, they will help but they cannot fix a leakage problem. Reduce humidity driven damage, yes, but not fix it if there is a lot of water entering.
I know quite a few folk who use them, larger than mine, and now swear by them. Odour gone or reduced and mildew reduced/gone.
Sorry for the tome.