I have a Mitsubishi MJe-16p and it is excellent though not cheap. Scroll down on this page: http://www.dehumidifier-humidifier.com/dehumidifier_uk You only need one for the whole boat and its big enough for a 5 bedroom house when not in use on the boat.
Seems that, unlike others, it will continue to work down at cold temps. I almost gave up and bought one last winter - but managed to find ways of coping (ventilation) without. Might get one next winter though.