I have not done this before either. But we have weathered timber over a winter.
I think part of it depends on your local weather patterns. Where I live in Canada when winter comes here it freezes and stays frozen till spring. No mildew should be possible except before freeze and after thaw. I suspect twisting caused by drying would be minimized during this time too. If the timbers or bents are stacked and covered to allow airflow and prevent moisture and ice buildup I suspect they will be fine except for some finishing work that would result from weathering.
