Jim/MoonShadows - I don't know how big your GH is, but when I had an 8x16 Rion, which had the "typical roof vents," I used cheap 3 mil clear plastic sheeting to cover it in the winter; it let the snow slide off easily without damaging the vents (and also held them down so the wind couldn't blow them open) - I think I probably added at least several years of life to that GH by putting the plastic over it in the winters.
