Would be interested to hear what Eskimo says about this issue. I have only used my QF3 three times (I love it by the way) and have a few spots where the same thing has happened. I wondered if it was the hubs rubbing against the fabric when being put away, or maybe ice scraping against it during setup/takedown. Last time out I went outside and left door flapping and when I came back in there was a streak of the gray inner coating scratched off on the door. I can't really figure out what would have done this.
Thanks.