How wide do you want it?
You could probably cut an outline out of a sheet of ply, match it and then put 2x4's across every foot ish. You would be able to make the rail as mellow or steep as you want it. I would think it would be pretty damn strong. At least the frame would be especially if you used 3/4 or 5/8 ply. 1/2 and probably 3/8 would work fine though. Especially with all the cross bracing.
If you did it like that you could make it anything from a few inches wide to a couple feet wide.
You'd have to see how strong the pvc was though. If needed you could go closer than 1 foot on the supports to keep it from cracking.
I haven't build anything with pvc in a long time but I would go with that route to make a rainbow.
If you had less than 2 feet of rise to the surface you could cut up to something like a 17' rail out of 2 sheets of ply. Having each side in 2 sections joined together.
I think it'd probably work pretty well.