There are a few full hookup campgrounds open year round in the northeast. Timberlane in Clarksboro NJ and Aces High in East Lyme CT are 2 that I've stayed at. There was a thread last year about Maine winter spots and we found a few there as well. A search may turn it up. Also, Allstays has an open all year filter and a few showed up.
As for weather, typically the first snow falls between Thanksgiving and the solstice but it doesn't stick (no salt put down). The first cold snap below freezing is usually not til after Christmas. Maine is the bigger problem weather wise. They are a week or 2 ahead of southern New England.
Propane won't be a problem. Aces High sells propane all year.
