Camp Chair Umbrella Holster

My roommate requested I build something to hold his umbrella while he sits in his chair holding his tailgate location on campus. After 5 prototypes, this is the version I settled on.

The holster clamps onto one of the poles of the backrest of the chair (I tested, and you can't even feel it). The body has four slots for 1/4" hex bolts. I use wingnuts as fasteners for convenience. A previous iteration had the hex bolts embedded into the body, but I decided that was a bad decision after one prin