I use Hoyer's mounting media to mount them, then sandwich the slide/coverslip between a strong fridge magnet and a cookie sheet (high tech, I know) while they dry to keep everything flat.

a quick and cheap way to mount wings is in 80% glycerol- "For analysis of wing trichomes, adult wings were removed, incubated in wash buffer (PBS and 0.1% Triton X-100), and mounted on a slide in 80% glycerol in PBS" ( Gault et al, J Cell Biol. Mar 5, 2012; 196(5): 605–621)

I agree with Mrs. Susan Younger, I usually use glycerol and after finished its the wing stored in micro-capillaries and both pipe ends are shield by wax