One scrim should be enough, wash it out regularly and wring it out by hand, thats how most Northern window cleaners do it. It takes a while to get used to wringing it out by hand, this way it won't be bone dry, but it will have some, albeit small amount of dampness so when you rub it over the glass it cleans perfectly everytime.....
Forgot to mention, use grade 2 scrim - that's what the Pro's use.