Last time I had to ship a rifle, I used a piece of large diameter PVC pipe, cut a wooden plug for each end out of a piece of 2x8, and then used screws through the walls of the pipe to attach the plugs to the pipe. The rifle itself was wrapped in a LOT of crumpled up newspaper, bubble wrap, and packing tape. After putting one end on, I stood the container up on that end and placed a lot of crumpled up newspaper in the bottom. After putt the rifle in the tube, I put packed a lot more crumpled up newspaper around it and then even more on top before I put the top plug in. I taped the plugs to the PVC pipe so that it would be rather waterproof. I then shook it and dropped it to see if I could get any rattle. Nothing... So, off it went to UPS after wrapping it in cardboard. Probably a bit overkill.