RE: Question building polyhedral wing, and wings in general
Use a bit of the scrap to make angle sanding blocks or jigs. Use only half of the total angle to make the block or jig then sand both sides as demonstrated. Some kits have these included.
If you have a table saw, or a bud with one, make a custom block with half the dihedral angle and half the polyhedral angle and use a biit of contact cement to stick on your paper.
You will want to use glue that lets you peel the old paper off.