The same thing happened to us last year in Spain it started at the side under the drivers door and worked its way in about 200mm. Its a very common fault with the ones with a seam. I actually did repair it and quite successfully and at the same time I was negotiating with VW about replacing it. It was out of warranty by about 6 months.. After refusing point blank to do anything my persistence worked. They agreed to replace the whole thing for a new one (without a seam) for £250. The dealer and VW paid the rest.. Ok it wasnt free but at least I have a brand new awning complete and fitted(without the seam) for £250...
I did actually put pictures up of the repair, I used "Stormsure" adhesive It worked perfectly but that didnt mean it wouldnt come undone somewhere else on the seam that you couldnt repair easily......Persistence sometimes pays off!!!!!!