This Eva-Dry dehumidifier came with our Nordic Tug, and we're impressed! One of these would be great in the Airstream during the soggy months in the Pacific Northwest, too!
It sits on the counter and runs quietly in the background, collecting water right out of the air. I usually empty it when it's half full or so, but it's got a little light that turns on when it needs to be emptied (and a shut off switch that turns it off when it gets full). The reservoir holds up to 16 oz of water, and there's a larger version if you want it for a bigger space.