I used to use the hairspray treatment too. White Rain hairspray. The cheapest, goopiest stuff in a can! and it worked. Sorta.

I spray my feathers real good with Scotchguard and let 'em dry overnight if I know it's going to be wet the next day.

One of the best things ever for keeping feathers dry is the Cat Quiver. Put the waterproofing on the feathers, stick 'em in the Cat Quiver. If you sit for hours with an arrow nocked up on the bow, the feathers will eventually get soaked, no matter what you put on 'em. If you leave them in the Cat, and only pull one out when you get ready to shoot, the rain will never have time to wet the feathers.

I hate wearing a Cat Quiver, but they hang quite nicely in the tree.