Roof bolt replacement - S3

[MWBS3]

Hi - I planned to have the rear plastic window replaced in the car - found a suitable chappie - agreed the price and went to remove the roof.
The bolts through the boot (ie hood frame to boot) - ALL- were rusted and siezed causing the bolt heads to rotate under the covering.
I wasnt planning on a new roof however I had to cut through the mohair and drill out the bolts.

Has anyone had this problem and how was it fixed please ?

My plan is to open up the mohair further ( scrap now anyway ) expose the glass fibre, dress it up and use marine epoxy resin and bond in 6mm stainless bolts. Then to the upholsterer.

Any thoughts ?

Thanks

Mark