When I was a kid, my dad was quite involved in Black Powder Rendezvous. Basically pretending you were a fir trapper in period costumes and competing against your buddies in all kinds of events. One of the events was starting a fire with traditional flint and steel.
Char Cloth was the standard Tinder. One thing we ran into consistantly was the cloth getting wet or damp. Because it is so dry, it sucked any moisture into it that it could. Rain, condensation, damp air... you name it. And being in the NW that's a constant battle. Wet cloth is obviously useless, and even slightly damp is just about as bad. Dry Char cloth works easily and extremely well. Do everything in your power to keep it dry. Especially if you plan to store it for any period of time.
We tried as hard as we could to dress and carry only kit that was available in the period. Eventually I started to store my Char Cloth in ziplock bags in my fire tin. It was just too tough keeping you fire kit dry running up the creek in the "Trapper's Run" or on a 4 day misty Winter Rendezvous. You may never have a problem, but keep it in the back of your mind.
Good luck... and keep your Char dry!
m