I had to cut away the flat section of arch that the rivets secure to the metal when I rolled my arches.
I used Tec7 sealer/bonder to bond them on. I put approx. 6-7 good size blobs (about 1" diameter and 1" high) along the length of the arch, then ran a fine bead of the same stuff along the edge.
I then used a variety of clamps ('variety' meaning what ever I could get my hands on) to clamp the arch in place for a few hours. When the clamps.....ah....clamp, a portion of the bead will squeeze out, make sure to get this off as quickly as possible. Will be a bit messy, but have loads of kitchen tissue/cloths at hand & keep using a clean section to clean off the bonder.
Others may know a better way, but that's what I've done.