I would only add two things to the above response. I would use an
etching solution such as Alumiprep 33 or Turco with the ScotchBrite,
rinse, then coat with Alodine, rinse and prime with a Zinc Chromate
paint before topcoating with a two part polyurethane. It's a lot of
work but your glider deserves it.

As for the shortcut solution, there are coatings which would protect
the surface but (at least for aluminium) I haven't seen anything that
would stabilize the corrosion that is already there.