My own IBC tank is outside, and after 3 winters I've not had a problem, though one time last winter, the water in my transfer hose froze solid

Tosh was over at the time, so we cailed up the transfer hose (all 35 metres of it

) and stuffed it as best we could inside an old water butt I was using prior to the IBC, then I got a fan heater out of the house, plugged it in and pointed it into the butt

Somewhat Heath-Robinson, but it did the trick

If you go for 100m of microbore (Gardiners) and a 100 psi pump + 2mm needle jets in your brush, yo uwill not need a varistream, and with an inline valve on your pole hose yo uwill also be able to regulate the flowrate without affecting the running of the pump.
Or at least that is the case with the Flojet pump, I don't know if the Shurflo version of the 100 psi pump is as robust as the Flojet though.
Ian
In the depths of winter, if you have a van, then some form of heater in the back is a good idea, I'm lucky in that I can have an extension cable out to the van 24/7, so I just pop in a cheap fan heater with a frosty stat setting on cold nights.