We have camped year-round in North Carolina for the past 8 years with no problems. But hardly ever in the mountains in Jan or Feb. Our underbelly is enclosed with ducted heat but no heated tanks. We've often camped when the nighttime low gets to 15 or 20, but in this part of NC it usually gets well above freezing the following day. So typically, no long strings of temperatures staying below freezing.
We make sure our holding tanks are never close to full, so there will be room for expansion if they do freeze. We unhook and empty the fresh water hose on freezing nights and re-connect it the next day. That's it. Never a problem.
Lots of people freak out about winter camping, but in this part of the country just a couple of precautions will carry you through. We camp every month of the year, so we end up winterizing and de-winterizing 4 or 5 times between trips during the winter, which is a 10 minute job and well worth it to be able to camp year-round. Go for it.
We camp at Swannanoa often during the year at a great campground called Mama Gertie's Hideaway. About halfway between Black Mountain and Asheville. It's open all year.
2013 Surveyor SP220
2010 Silverado LT 5.3 V8
The world is a great book, of which those who never stir from home
read only a page. - St. Augustine