It also seems that a wool fabric would make a good weather sock.
I originally thought, and may still pursue, an under quilt protector of DWR material like the M50 and then fashion a top cover of a wool blend or even tropical weight wool. But I also like Lost Biker's idea of a lightweight nylon for both it's low cost and utility. There's a source for 1.1 military camo for $1.25 a yard but it's in rolls. :-(