Cotton balls with Petrolium Jelly make a waterproof tinder. When I demonstrate fire making, I soak a CB/PJ in water. Remove it from the water, shake the water off and light. Burns great, but watch for the remaining water drops to "explode" with hot bits of CB/PJ and boiling water. Never tried it after taking the CB/PJ to any real depth of water though. Give it a try and report results please.

Nomad