I have the dry mouth problem, too. A couple of things that have helped me are hydrating before the dive by drinking Vitalyte (it's like Gatorade but without all the sugar) and by getting my reg wet during the dive whenever my mouth starts to feel dry. A former instructor taught me how to do it; don't know if you've tried it or not. I take my reg out of my mouth, hold onto it for a few seconds, then pop it back in my mouth and clear it. The water that's still on the reg when I put it back in my mouth is enough to take care of the dryness for a while. If you try this, be sure to blow a constant stream of bubbles while the reg is out of your mouth since holding your breath while diving is a no-no, as you probably know.