We use a small dehumidifier similar to the one you mention, and do notice the improvement inside the boat. However we were told to keep a little heat on too otherwise the cooling plate in the dehumidifier will freeze and it will stop working.
I check the boat regularly - twice a week at least, and leave the heater on "warm" rather than the hotter settings... keeps the boat at around 12 - 14C when it gets close to 0C outside. The reservoir in the dehumidifier gathers about half a liter(quart) in a week of soggy west coast weather.
Overall we're quite happy with this arrangement. SD is correct in the need for ventilation, so if security concerns allow, leaving a
hatch cracked somewhere helps keep the air moving. We have also, in the past, hung a couple of computer "muffin" fans to move air around.