Our Northern Polytunnels 21 by 42 foot tunnel, 12 foot high, has lasted 15 years of mighty gales, thick layers of snow and the occasional hole poked in it. The hoops are made of a thicker metal and a slightly larger diameter than standard, specifically to cope with northern weather. We also bought corner braces and crop bars to help stability as well as for the crops. We have changed the cover twice and replaced the base rails a couple of years ago, but the tunnel itself has been superb.