We winter camp here in NC quite often. Our trailer has an exposed underbelly and a portion of the plumbing is also outside along the frame. We get cold enough at night that we just leave the trailer winterized and use bottled water. My biggest concern with the black and grey tanks is the outlet pipe freezing near the valve. To that end I put extra antifreeze into the grey tank so we can use the kitchen sink but for everything else we use the campground facilities.
2015 F150 Ecoboost
2014 Palomini 142 CK