I'm getting a visual on the direction you are going here and what I'm proposing is to only get you close in seeing how much work you need to do. This is only a ballpark or basic start, and maybe you don't need to do as much as you think.
I get lots of folks walking through the door with products to bend and I need to determine the angle(s). If it's bent then it has a radius and if it's rollformed it usually has even more radius. An example might be a roof flashing for a penetration through a metal building roof panel. There are usually some constants here, like center-center of the ribs, height of the ribs etc and I have to take into account any stretch or distortion. My reference here are ribs that are truncated cones, or in your case, the Vee's. With that said; I begin with getting an approximate angle using the flat of the panel up the side of the rib. I take the centers of the ribs, the base dimension of the ribs, the flat (truncated) across the top and with a little math determine what the angles are, what the stretchout of the flat piece should be (hopefully).
Now to your project; After the preliminary task of getting close, I shear, notch, and spotweld a template that fits the panel shape before I shear and bend the real thing. I think you can see an end view of a one piece template that fits the bed as Bob explained, and if you need any help with coming up with a template just PM me. Many times I take strips of metal (16 ga.) and vicegrip them together as I work through the angles, by placing the pieces against the shape I'm measuring or attempting to determine an angle. If you get a good fit across the unworn section of the bed, then you will see the daylight on the worn sections.
As I stated, this is to give you an idea of what's on the road ahead, before you go to Bob's #9 post. Okay, and I see I missed Ken's attachment for the fixture, and in essence that's my idea but at a basic level to start.
I get lots of folks walking through the door with products to bend and I need to determine the angle(s). If it's bent then it has a radius and if it's rollformed it usually has even more radius. An example might be a roof flashing for a penetration through a metal building roof panel. There are usually some constants here, like center-center of the ribs, height of the ribs etc and I have to take into account any stretch or distortion. My reference here are ribs that are truncated cones, or in your case, the Vee's. With that said; I begin with getting an approximate angle using the flat of the panel up the side of the rib. I take the centers of the ribs, the base dimension of the ribs, the flat (truncated) across the top and with a little math determine what the angles are, what the stretchout of the flat piece should be (hopefully).
Now to your project; After the preliminary task of getting close, I shear, notch, and spotweld a template that fits the panel shape before I shear and bend the real thing. I think you can see an end view of a one piece template that fits the bed as Bob explained, and if you need any help with coming up with a template just PM me. Many times I take strips of metal (16 ga.) and vicegrip them together as I work through the angles, by placing the pieces against the shape I'm measuring or attempting to determine an angle. If you get a good fit across the unworn section of the bed, then you will see the daylight on the worn sections.
As I stated, this is to give you an idea of what's on the road ahead, before you go to Bob's #9 post. Okay, and I see I missed Ken's attachment for the fixture, and in essence that's my idea but at a basic level to start.