We live in Coastal Georgia and use our RV year round. In a normal year, winter lows hover in the mid to upper 30s to low 40s. Lows in January sometimes can dip below freezing. Usually in February, there are a couple days that will deep into the 20s. A few times we've had lows below 20.
What I normally do when we are between winter trips is blow out the lines, drain the hot water heater, make sure the holding tanks are empty and drop some anti-freeze into the traps and the toilet. It doesn't take more than a few minutes to fill the fresh water holding tank.
-Michael