The cloth material does fine in the bitter cold. The window also does fine if you aren't using it. If you're opening it and folding it, it just gets brittle and can crack. The other option is a mesh back window, but then you'd get a ton of dust in the bed, so I haven't tried it yet.
I have left my truck outside in some pretty good wet snows. I've only had it for a couple years, so I think the biggest was about 10". The metal frame is pretty solid for static loads spread evenly across the top, especially when the material is tight, so I wouldn't be worried about snow load unless you started talking pretty crazy amounts like over 2 ft.