I left extra to wrap aroung the edges, and it is tucked in, so I can't see it peeling anywhere...The sagging just comes from the foam deterioration over time.

I had nothing when I bought the truck. There are even 2 little support bars under there that rivet to the roof rails. I put it up and realized the 2 plugs in the middle weren't hitting anything. I had to call the guy back, get the bars, and pull the liner back down.

A tip for someone thinking about doing this is you have to have at least 60" wide material, 2 cans of quality adhesive, and spray the fabric and the backer with glue. Other than that, it was easy...