what I did last year
I drained the lines with the low point drains.
Put the HW heater in bypass mode and drain.
I used an air compressor to blow lines, this seemed of limited use since there seems to be a check valve inline that seems to limit the air flow.
Replaced the filter in the fridge with a dummy pass through.
Ran pink stuff through the lines and the fridge water supply.
Ran the washer to get some pink through both supply lines.
The system kept enough pressure that the ice maker cycled and made some pink ice, I then knew that the line to the ice maker had pink in it.
we survived the winter without any issues
When we took the camper out during the cold season the fridge water and ice were not used, I just had to flush the lines when used and then rerun the steps, leaving the fridge out of service. There is a cut off valve buried back behind the pantry, I have not used it.