There are hoses with heat tape surrounding it so the water never freezes. Even with those hoses, you can have issues at the spigot and inlet if allowed to freeze. Drawing from the onboard tank will reduce the concern over a standing water line in the freezing weather. You should't have any issues with the hose so long as water is running such as when refiling the tank.
Small heat pads on the waste tanks is the best solution if planning to camp long-term in freezing temperatures. Even with full hookups, you still wave water standing in the lines. Most tank treatments delay normal freezing
so unless your taking always freezing, not that big a worry for an occasional overnight freezing temps.
