I lived in a 37ft, insulated camper 4 days a week for 5 years in the bitter cold of winter and found it is quite necessary to prepare the camper and the connections.
I had 3 electric heaters going 24/7 and the propane furnace
set should the electric heaters go out. (Furnace ran off of the 12VDC system). (Electricity was provided free at the camp ground).
Leave all cupboard doors open where water pipes are located. Put heat tapes on the outside exposed pipes of the camper to include fresh, Grey, black in and out lines. Even with all that heat there were times that I had to leave the faucet in the kitchen dripping to prevent freezing.
Be sure to put a heat tape on the water supply hose that goes from the camp ground to the camper otherwise that will freeze and burst. I know it says on the heat tape to not cover with insulation or to use on a hose however I put the foam water pipe insulation over the heat tape that was wrapped around the hose and had no problems. You CAN NOT have a heat tape cross or overlap the heat tape because it will melt and short out at that crossing.
I also put rock salt in the grey and black tanks and had heat tapes on them also. They were exposed underneath the camper.
Because I was there for so long, in year 3 I put a black, bendable, semi-hard PVC from the camp ground connection (bib) to the trailer along with the heat tape and insulation. This was possible because I was not moving the camper and it gave me a little more protection. I had a 50psi limiting device at the camp ground bib so it would limit the water pressure to the hose and camper. If you install this device at the camper instead of the camp ground bib, you stand the chance of the water hose getting hot in the summer and pressure over 50psi may balloon and rupture the hose.
Good luck and good camping.