@Poppo I also get dry, cotton mouth (though admittedly probably for different reasons 
). I find having a nice cool glass of water by my side helps tremendously to keep my mouth fresh and moist.
Maybe this seems too obvious, but I also have had sore, dry lips after playing for a long time. Licking them seems to only make the problem worse and for some reason I’ve never been a fan of lip balms or Chapstick.
Maybe we need to just tough it out, keep a “stiff upper lip”, but relaxed, as @Luke suggests 
and build up callouses on our lips as guitar players do on their fingers . Just kidding, that sounds painful hahaha.
Water works best for me to keep my lips slip sliding along da harp 
.