For those that have issues with dry mouth. Try Biotene Gel. It don't taste that great, but it works great. Biotene has a whole line of stuff for dry mouth but the gel lasts the longest throughout the night.
I use an APAP with the Respironics TotalFace mask. My septum is crushed and I can't breath through my nose, so being a mouth breather full time meant finding a solution to dry mouth was pretty important.