I'd be interested in what others do also. We own a 36foot sloop that, normally, we keep in the water over the winter at Seward, Alaska. We've owned her for two years now; this coming will be our third winter. Thus far, the only damage we've suffered has been a broken head. Temps at Seward get as low as -10 to -20 F. but don't stay down that low for long.
We puts tabilizer in and fill the fuel tank, empty out the water and holding tank, put in about 5 gal of the pink RV antifreeze and run it thru all the faucets. We flushed about a gal or so down the head and that's about it. The engine is fresh water cooled so I check the antifreeze with an automotive antifreeze tester (kind of a basting bulb with a specific gravity meter that rates the protection level). We strip off all of the sails and canvas, cover the main companionway hatch with a tarp (to allow us entry without dumping a bunch of snow inside) and that's about it.
Once a month or so we trundle on down to Seward (we live in Peter's Creek, about three hours North) and camp out on her over the weekend. Makes for a good winter retreat.
I'd be interested in hearing what others have to say, though. We're still pretty green at this and welcome suggestions from more seasoned hands.
This'll be the first year she's wintered over on the hard.