SWB Fleetside bed question

[Joyridin]

Somebody put a tonneau cover on my bed years ago. I guess back then, they weren't to caring about how it was installed. They put the snaps on the outside of the bed about 3" from the top of the bed.

Well, I removed them, welded up the holes, and filled it. My question is this: Are the sides of the bed flat, or do they have a very slight out outward radius to about the center of the wheel arch, then radius back in? If they are flat, I have a heck of a lot more sanding. If they are slightly arched outward, then I am probably done.