Great idea! You must be a plumber to have that red rubber gasket cap around to use. If you toss a couple of dessicants from new boot boxes into the tube when you seal it, the bolt should be very well protected.
Now that you mention it, I do get roped into plumbing jobs fairly often. :-) I’ve had to repair enough drains to know that those red gasket caps were available and me and one of my boys marched our happy selves over to Lowes... took a bolt with us... and found that 1.5” PVC was close enough. I made two of them. One for the CMMG bolt, and one for a spare bolt that I have. I’ve been wondering if the storage tube will float and leak. I don’t think so because it’s pretty tight when sealed. But I haven’t tested it “yet”. :-) I’d like to devise a way to attach a small length of plastic cladded steel cable to the cap so it can’t get (easily) separated from the tube... but that’s another small project. :-)