[Butch Cassidy Slept Here]

I'll assume the reason the military hasn't issued a waterproof duffel is because the current cloth/canvass issue is lighter. If someone is chasing you, or vice versa, I can appreciate the need for quick, unimpeded movement.

Springing for the big bucks, and making a trip (or on-line order) to Cabellas will probably yield a soft sided duffel, or other bag, built to hold-up to downpours if that's what is needed.