bildan wrote:
If the glider is tied outside, taping some plastic sheet over the
spoilers will keep water out.

Eight short pieces of duct tape (one for each joint) seal them pretty
well and are a matter of a few seconds. At least that's what I do when
for whatever reason I have to leave a glider outside overnight. Every
glider pilot should have a roll of duct tapy handy, anyway.

That said, I consider it pretty cruel to tie a plasic glider outside.