I misread your post, for some reason I was thinking you were removing the propane
tank & not having propane
, instead of just taking off one of two tanks. Can't come up with a solution now......maybe a regular battery box would fit in front of the tanks, hard to tell from the photo & how the crank handle of the tongue jack would be in the way or not of a box there. But this wouldn't give you the added storage.
If the 'Lowe's' box would fit where the tanks are & leave room in front for one tank, it would be a neat set up.
As for the CPAP machine, I have been using one for about 6 months now. You said, he feels like he can't catch his breath with it. At first I had a similar feeling as if I had to remember to breath, but I just kept at it & that feeling soon went away. Has he tried a Nose Pillow try mask?
After trying 2 masks, I got one which is some like one of these ResMed Swift Lt CPAP Nasal Pillow Mask with Headgear
A Nose Pillow they are called, it really works well.
Maybe if he tried one of those he will get used to it easier. Much healthier for him if he would use it. Mind over matter, got to believe one can do anything to conquer it.
Good luck on both matters.