A few tips for anyone with cold WFP to keep going.
Don't worry about the hassle of an immersion heater in your tank. Just run a 3kw fan heater in the back of your van for 20 mins or so before going out - will defrost any frozen hose etc.
My hosereel is bolt down in back of my van but if you have freestanding then leave it inside the back of van where the warm air is.
If you have custies with bigger houses where u can park on the drive - leave the engine running while you do the job with the heater blowing warm air into back of van - no freezing up - worked -3 yesterday with no probs. Its like heating your hosereel.
If you are at a single site like i was today - keep a 30m extension reel in van with your 3kw fan heater, then hook up to custies power point and leave fan heater running in back of van.
Always depressurerise your system at end of day and unscrew your strainer housing and empty water, and also release your female connector from hosereel spindle and let some water drain out, so they do not crack if water freezes.
Always bring your poles and any other gear you can inside overnight. Get your RO system on asap when you get back in to refill tank, once its running it will not freeze.