As trailer builders, we often have unusual inside and outside shapes that need sanding. Standard sanding blocks or just a hunk of wood the size of the sand paper just doesn't cut it. I found a smooth, black rubber base to a traffic deliniator that was layin in the road with no deliniator in sight. It is about 1 1/2" thick and nice and solid. Someone must have discarded it and was definately a traffic hazard, so I picked it up.
After scrubbing it down, I cut it easilly into various tapered shapes on my bandsaw, into inside and outside curves that work just great for holding the sandpaper in just the right shape. Now I have about a dozen of them to suit whatever condition encountered. Works great, give it a try.
Roly....PS, don't rip them off at a road construction zone, after all, the fines are usually doubled in those areas.