OK.. here's my plan...
I have a stuff sack full of.. stuff sacks. I have a few very small Sea2Summit bags that are just a tad too small for the InReach, but good enough to see that it will work. I've been making round bottom stuff sacks for my various cook kits so I am going to sew two of them the right size for the InReach. I am also making two mesh water bottle holders for the shoulder straps since I recently changed my water filtration and storage.
In the interim, I am going to ranger band the small stuff sack to the shoulder strap..