My suggestion, but only if you don't want cheap, is PolyMetal or equivalent.
It has two skins of aluminum about as heavy as a beer can (.007in) separated by a plastic sheet. It's described as rigid as 5/8" plywood but 1/10th the weight. I bought the samples in the picture new, but since then I've found larger cut-offs at the recyclers.
You can shear and roll it, but as you see it doesn't brake very well. It's stiff enough that you wouldn't need many attachment points. There are other rigid panels as well, like the material they use for commercial rest room walls.
If you work with coroplast try laminating two sheets with the flutes crossing each other, it might not sag as much.