Have I found a solution for full face mask users?

[jomama]

If one can't learn the tongue trick, then it would be beneficial to make peace with a FFM.

To repeat, I do have a FFM, and I get dry mouth from it, too, even using the humidifier. 

What kind of mouth guard keeps air from going in/out the mouth?

[avis]

I enjoyed reading all the serious post of my friends. Your posts give me the idea to invent a product to put in the mouth and hold the tongue in the right place. What do you think?

However, my first advice is to be sure that you have free airflow from your nose, otherwise you better breath through your mouth. I emphasize that even it's clear and obvious.