Has anyone used a 12v ceramic car heater??

[rash_decision]

Hi, I've been looking at getting a heater for my boat, and have been drawn to these little 12v ceramic type heaters. They are only 150-200 watt, but I'm unsure if this would be warm enough to heat the cuddy on the boat? It's probably about the same size as a large saloon car's cabin, not very big really.

Has anyone used one of these with satisfactory results??

Similar to this one

http://www.ebay.co.uk/itm/12V-PTC-CERAMIC-CAR-HEAT...