Hi
I had a quick look at your bio
Well done for getting through treatment and into remission
I am 16 months out of RT and doing well but as you say the dry mouth can be troubling.
My go to solution is chewing gum sweetened with sorbitol which protects your teeth.
Amazon sell Peppersmith gum which is ideal as it doesn’t have any other sweeteners.
I find I don’t have to chew it all the time simple park a piece in my cheek and chew now and again.
I also had a course of acupuncture which really did the trick while I was having it. I will restart when my practitioner is back in her clinic. There is a separate protocol called Auricular Acupuncture for xerostomia.
If you do have some saliva Then xylimelts help you get through the night. These are little tablets of xylitol that stick onto your gum and slowly release through the night. I started with two and now just have one.
You can get these from Amazon too but Google might find you cheaper outlets.
I keep a glass of water by the bedside and I have got quite adept at taking a sip when needed then falling straight back to sleep. Practice 
Time is a great healer and the situation does get slowly better though never back to normal.
Hope this helps
