I also purchased one of these polytunnels. Seemed like a good buy at the time and taking their description about 'high quality' and 'tough pvc cover' convinced me this was a good starter solution for someone starting off in polytunnel gardening. Six weeks later the tunnel lies in shreds and my plants which had been doing fantastically well ruined. The basic design of this tunnel is flawed. The weak points are the seams, where two sheets of polyplastic have been stitched together. First gust of wind and they just rip open, the whole seam is just not strong enough to withstand wind. The ties and guy ropes actually accentuate the strains on the seams and there is no real way of fastening the edges around the base of the tunnel. Even the metal eyelet (one at each side of the door at both ends) sheared from the plastic which was supposed to be holding it.
Despite extensive searches I have not been able to find replacement covers at all on the web or Gardman's website. Not that I really want another, but I need to get some breathing space to try and salvage some of my plants. MInd you at least I was lucky. I got six weeks out of mine. My neighbour only managed less than two.
Unless you live in a vacuum or plan to put this up in a garage, I wouldnt waste your money.