12v dehumidifier

blaczero wrote:
Do they exist?

well, some that are peltier devices do exists, but they really don't do much.

If humidity is high enough that you need a dehumidifier, then you need one that has a compressor, basically they are an AC unit, air goes over the cold coil, water condenses, usually they can pull several gallons of water out in a matter of hours. They peltier devices might get a few ounces out in the same time.