PVC is the way to go. Do you have pics of the mounting ribs? If it is solid wood, christmas tree clips will work. What do you mean by "solid metal ribs" ? Here are some of the clips I use.
Go to Rockler.com and check out a product called "bendy MDF" it's a medium density fiberboard, sort of like untempered masonite and it is supplied with saw kerfs in it already. I soaked it with a spray bottle and bent to my hearts content. Just keep it formed till it dries. After it dried, I laid it up with a layer of fibergl*** cloth and polyester resin. It gets real strong and holds its shape beautifully and you can have it delivered to your door.
Go to the source, I say. The Plywoods live just two blocks over, so I asked Luan, myself - careful that she knew I was asking on behalf of 5window. She laughed. "I have a husband and three kids. Maybe back in high school, but no, not now.... but do tell your friend that I'm flattered that he's interested."
Thanks for all the advice. Here are a couple of photos of the A's interior. Hopefully, you can see the bend at the rear corners and well as what I have to attach it to. Attachment points will at at either very hard,aged wood, or solid metal. I'm not sure how the Auveco spring clips would really work, although I might be able to router keyhole slots at some places in the wood. Thanks again.
FWIW, The grey flat panel at the lower right of photo 3 is the panel dividing the trunk form the cabin. It is the old grey vinyl over 1/2" plyoowd with about a 16 ga sheet metal panel on the trunk side which is then covered with the trunk carpet.