Another Alternative
Depending on how much you plan to use your boat in the winter, another option that is much, much cheaper is a small wood stove (mine is made by Dickinson). I mounted it on the aft end of the starboard locker as others indicate. There is little room down low or in any other areas. I burn presto logs and can get the cabin quite toasty while at anchor or while sailing for that matter. It's not a cadillac system like the forced air, but you can do a nice neat installation yourself for about $600 total cost. It's totally quiet, uses no power, doesn't require you to run your engine, etc. It's not for everyone. I wouldn't advocate it if you planned to live on your boat. But if you sail for the occasional winter weekend or extended weekend, it can work well. During the remainder of the year, it takes the edge off a cool night. In terms of the concerns raised about mounting it on the wood locker, I had some custom shields made that protect the wood and the cabin ceiling penetration for that matter. They are stainless steel sheet metal shields with ceramic fiber insulation behind them. You can make templates out of cardboard and then have a local company that makes duct work and other sheet metal fabrication build them for you. I live in your neck of the woods, so just wanted to let you know that you can make do with a volkswagon for a lot less than the cadillac forced air system. Good luck!