Finally fixed it. I couldn't get any of those well nuts in time so I used a M6 aluminium bolt and one of those Audi anodized nuts filled in with silicone rtv sealant and a nylon washer and tightened. It was a right pain to fit the nut and tighten from the inside but surprisingly can be done by one person.
Then filled the whole area where the original fabric patch was with more silicone.
Sorry this pic is upside down