Yes, Ray, they are. Problem seems to occur when the weather heats up. As for dragging them, I have always kept a plastic cut-out cushion under them as per your instructions. The leaky hole, however, is not really the lowest point or at least doesn't bear the scratches that the outer corners do.
So I don't think it's a result of being scarred/scraped...just very thin plastic to begin with that stresses when the temps get into the 90s. You can see that by the picture - very thin in certain areas, probably due to the molding process itself.
While I can get my money back, it would be hard to replace right now. So I need a repair solution through Sept. I did find this interesting article:
http://info.craftechind.com/blog/bid...ue-for-Plastic