if i were still roofing i would have used epdm rubber roofing to do it, it was all i could think of at the time till the bag came to mind.
epdm is like a rubber tire tube material that you glue up like rubber cement, brush on both side let it dry and press together, it would have lasted the life of the car, but it ain't cheap and didn't have any, so the bag went in.
so i did have a better idea how to fix it but not the supplies. the bag wont last for ever that's for sure.