I don't know about small dehumidifiers but I am wondering about the source of all of that moisture. How dry is your bilge? If you have water down there, that would be a big source of your mold / moisture problem. Drying that up would clear up the other problem. Usually, providing ventilation is sufficient to avoid moisture and mold. Maybe a Nicro solar powered vent in the cabin?
I'm votin' with Tod; that's a good summing up.
We have virtually no mold/mildew in our boat nowadays. Not so when we bought it. Note that once those spores get established in all the damp and hidden places -- some almost beyond your farthest reach-- it's really hard to get rid of them. Hard cleaning work, but it really pays off.
Having said that, what you need to do is use any standard cleaner/disinfectant to really clean up all reachable surfaces. And, I mean all
. Pull out everything from under settees and everything from the bow stroage and all (!) lazarettes. Scrub and clean and towel dry.
From that time forward you Absolutely Must keep the interior DRY
. Yup, capital letters, as in 'shouting on the internet'.
If you have deck or cabin leaks, cure them. If there's any water in the bilge, find out where it's coming from and put a halt to it.
Equally important, ventilate the boat by allowing inside air (usually damp air) to exchange to the outside. Then, even more important, establish ventilators for EVERY hidden area under ALL the settees and other areas that are enclosed now. Your below-waterline hull areas will (!) support condensation and if there's no way for that moisture to move into the air, circulate, and exit, it will feed new mildew outbreaks all over the place.
Our boat was a virtual mold farm when we bought it. (It had sat closed up for three years.)
We had to launder all the cushion covers three times and put new foam in 'em.
I added two Beckson ss ventilators for the aft cabin and aft head. Good news is that our Lewmar hatches have a latched "vent" position and that's where they stay unless a storm is in the offing.
Equally important, I added a total of ten plastic/ss vents under every
part of the interior that had formerly been isolated from air turnover.
In the mid-90's I changed out the old stuffing box for a PSS shaft seal. Bone dry under the engine ever since.
We are in a Very
damp climate here, almost year 'round. We also have a boat with a keel stepped spar, so there's a quart of rain water in the bilge after any decent storm. I use a "turkey baster" to remove that water each week.
When I roll back the hatch and open up the interior there is NO "boat smell". I like it that way, and more important, the Admiral likes it that way!