A hint I was given by professionals repairing and repainting long glider
wings. Use a 1 metre long extruded aluminum veranda post for a sanding
block.  Attach the paper using double sided tape. The veranda post is 50mm
wide square tube and very importantly has rounded corners so it doesn't grab
or dig in during sanding.  Always move the block at 45 degrees parallel to
the spar. I was surprised how many high and low spots I found using this
method.  Hopefully at least the top surface will be ripple free when the
paint job is complete.

Chris Moore

LNC2 90%