This is in MN.  2 weeks after installing a replacement heavy duty cover , a 60-80 mph windstorm knocked over a  willow  tree directly on the fabric shed.   When the neighbors called I expected the worst.  The cover did not rip and the frame work maintained  is shape.  The tractor was driven out and  used to lift the tree off the shed after some initial trimming to eliminate some of the weight of branches and trunk.  I again stretched the cover and checked the anchors on the frame work.  What a product!  I was told the heavy duty cover would stretch and be much stronger.  It certainly is.  I expect no problems from the snow load  in the winters to come.