Underwaer are overated anyway!
No use for 'em while camping.

Interesting...."back up for bag getting wet"?  Mine would be to "dry it".  I've never had a situation where the bag couldn't be dried.  Has that happened to anyone else here?  I guess I can imagine a few scenarios where I'd be looking at a wet bag at night.....yuck!  And if it got cold....could be disasterous.