First, is the boat completely leak-free, with a dusty bilge? If not ventilation is the best approach and it's never going to be that dry.
Second, is the boat on the hard or floating with power hooked up? On the hard options are limited to adsorbants and absorbants.
If you are in the water with power hooked up, then guess what, you already have the charger and sump pump running. I don't see how a small dehumidifier changes much. Not a big compressor unit, just something suitable for keeping a dry boat dry.
I've been running these for years (also a similar Perfect Home model). They draw about 75W and are quite unlikely to overheat anything. They can be run in 12v, although they may be safer on 120v (lower amps).
I wanted some measure of dehumidification during the brutal nc summer. I have always used those absorbants in a variety of reincarnations. I was not happy with them overall ... The potential mess, and the constant replenishment.
I began the search for a new humidification system. I had a few requirements
Large reservoir. I Close my seacocks when away from the boat so it had to be able to hold a fairly large amount of water.
Auto shutoff if the reservoir is full. Just in case.
12v operation. I turn off all of the breakers when away from the boat ( except for the charger and bilge).
I don't think I mentioned it but the dehumidifier i used (and all Pelletier based dehumidifies that I looked at) run on 12v and come with a transformer. So these can be run on 12v DC or 120 AC whichever you prefer.
Note: I may switch it to AC based on pdqaltair's great write up and his mention that they might actually be safer on 120
It works great, seems to remove plenty of water, and has a very large capacity.
"Looking for clever solutions to keeping humidity out of the boat whiles it's not use. The wife wants to leave a humidifier on and running "
Heheh. One might suggest keeping the wife off the boat and away from any power tools if that's the case, a humidifier would just make the boat wetter. (VBG)
The buckets of "Damp Rid" and other chemicals will work but you'll have to keep swapping them out as they go liquid. Other than that...I doubt "natural" ventilation would be enough, even with dorade vents or solar vents but that's all you can try, unless you go to a powered system with a dehumidifier in a sealed up (no ventilation) boat. A small dehumidifier, enough solar panels to power it averaging out with your battery bank...if the math works there's that to try as well. It might take a few days to catch up and dry out the interior before it ran at a lower rate, but there are no magic options.
"Damp Rid" also has a hanging unit that is completely self-contained. Large capacity and works great. We deploy three of them on our 30' foot when it's hot out and we're away. Never an issue with odor, mildew, or like.