Update - awning replacement has finally been approved. I went through customer services, who contacted the dealer (who had already rejected the claim for a warranty replacement), who then contacted me. Customer services required the dealer to take their own pictures of the issue. My pictures were, surprisingly, not sufficient evidence.
I duly visited my dealer yesterday, because it was a predictable sunny day, which was necessary to "warm" the awning and therefore demonstrate the problem. Unfortunately, it was quite chilly, so it was a poor demonstration. The creasing was quite minimal.
It seemed that one of the reasons for the claim being approved was, in addition to the images, the dealer was satisfied that I was handling the awning correctly and the issue was not caused by "owner abuse".