Winter RV camping

I live in Middle Georgia...full time Rver...but I stay on a private lot...do not travel....we do not have cold cold winters, but cold enough...The camper I purchased had a bad fridge, so took it out and replaced with a dorm size fridge, utilized the space and built a pantry in its place...my question is concerning holding tanks...how to keep them from freezing, i leave my grey water tank open and water running inside, since I am hooked up full time to a septic tank...would underpinning the camper help or hurt, to keep the winds from the tanks...just wondering