I’m finishing up a plane that’s been dragging on (don’t have a lot of time working two jobs). Of the three flaps, one fits absolutely perfect, one has a smooth concave warp along its length, and the ends of the third warp “up” at the trailing edge. I made the flaps a while ago and let them sit, fortunately they have no sealer on them.

Anyway, I thought about pinning them down and then fiber glassing (fuse has water-based polyacrylic over ¾ oz cloth, as will the wing) to straighten them out, but thought I’d check here first.

Add some balsa to fill in the warps. Re-sand and finish as usual back to the original straight shape.

sounds like it would work, have you tried it?