long curved body panels

[warren57]

I'm asking this question for my brother that installed a new rear qtr on a 71 El Camino and decided it was a great idea to weld the top to the bed all the way across in lieu of spot welding it on.
Now he figured out why the factory panels are only spot welded at the top flange under the molding, but now having difficulty getting the waves out.
When applying a skim coat the length of that panel, from nearly top to bottom, it's not easy to sand it and keep it flat. An air file is of no use because of the contour.
Any ideas how to sand such a thing? Needs something like a curved sanding board 2-3 feet long.....
Appreciate your thoughts. All I keep thinking is maybe a long straight radiator hose with paper wrapped around it...

[Rick_L]

That works, as does an appropriate diameter of PVC pipe. You can also put foam pipe insulation over the pipe. Rigid is better when leveling the filler at first, something a bit softer is better to finish up.

[DoubleNickle]

Rick_L, what size PVC pipe would you use?

[Rick_L]

Something that matches the contour pretty close.