This print is to hold a CPAP mask and an additional headband.  The shelf is flat on top and curved on the sides to brace the head tubing properly. 

This is designed specifically for the ResMed AirFit P30i Nasal Pillow mask but will hold any mask easily.

I included two prints, one has an additional hook located under the shelf.  I use that to hold the head strap need to keep your mouth closed.  The second file has no hook.

I was able to print it with no supports needed if you print it with the side that attaches to the wall facing down.  I used 2 x #6 x ¾" screws to attach to the headboard.