Yes, use PVC pipe/tube sized to your barrel. Wrap the barrel with paper – 2 layers is fine – and use VERY tightly wadded balls of paper at each end. TEST the capped package before tapping the second end closed – if the barrel moves when shaken HARD end to end, add more wadded paper at the end (second cap end). When you’re done there should be absolutely NO movement when very vigorously shaken end to end. Tape the caps over the ends along the length of the tube and then tape around those lengths of tape.

Do not tape over barrel threads (unless you really enjoy cleaning off the glue from the tape, typically duct tape – that glue is NOT a substitute for anti-seize). Instead, wrap several layers of paper over the threaded section(s) and tape that wrapping to the OD of the barrel. Cleaning off a “flat” surface is simple and quick.

Finally, if you use USPS (I do), consider letting the clerk at your PO affix the label so the bar code orientation best matches PO equipment – then (you) clear-tape over the label (with the tape gun you remembered to take to the PO).