Here is how I keep my pipes from freezing.
I call it an "Active Antifreeze System".
The idea is to detect when the pipes are getting cold and then run hot water through them to warm them up. So you don't loose any water in the process you create a loop in the hot/cold pipes.
You need a thermostat and an electric valve to make a loop out of the plumbing. You start at the far end of the hot water pipe, through the valve, and back to the input to the water pump. Both ends tend to be in the same place next to the fresh water tank.
I looked at the plumbing in my RV and it ran from the fresh water tank to the pump, bathroom sink, to the other side under the floor (a freeze point), to the shower, the toilet, on to the kitchen sink and then into the hot water heater. A hot water pipe then went back the other way and ended up at the bathroom sink in
the same compartment as the pump.
I added a thermostat, an electric water valve, a short piece of plastic pipe, and two pipe T's to the system. The thermostat was placed over the pipes in the floor and under the bathroom sink It would react to the temperature in that closed in space with the water pipes. This space also happened to be on the floor with the great outdoors on the other side and under the RV (a freeze point).
I cut the hot water line as it went up to the sink above and inserted one of the pipe T's. The other pipe T was inserted in the water line as it came from the fresh water tank ahead of the water pump. New plastic pipe was used to connect the hot water T, through the electric valve, to the fresh water tank T.
The wiring included hooking up the thermostat to some power and on to the valve.
When the temperature got below 40 degrees or so, the valve would open and water would circulate from the end of the hot water line back to the outlet in the fresh water tank (input to the water pump). This would circulate hot water through the entire length of piping until the thermostat got warmed up and the valve would close.
No freeze ups since I added this "Active Antifreeze System".
A side benefit can be had by adding a push button switch across the thermostat so that pressing the switch will cause the valve to open. That way you can bring hot water to the furthest point without wasting any water waiting for it to warm up. A useful function to save water even in the summer time.
An "Active Antifreeze System" can be easy to do if the layout of the plumbing is appropriate.