get rid of the tank and get a 50L TROLLEY then you wont get any freeze ups or messing about with heaters in van.simply bring it in every night and put it on charge(i do that every night anyway!
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do bottoms trad if cold and if there could be freezing water on the ground issues and carry a bit of grit with you to put down on paths etc.
if VERY COLD then have a day off!if its persistently bad with snow then use your trad pole on first floor windows with screenwash in ya bucket if you really need to work!
get some good gloves!(ive got the glacier perfect curve and find they do keep ya hands toasty!).
oh and i try and get a half days cleaning in on bad weather days as 6 half days in a week is better than nothing if its bad all week!
this will be my 17th winter window cleaning!first one wfp!last year was by far the worst but hopefully we wont get another like that for a while!
regards
dazmond