I pack them in a plastic Benelli gun case adequately padded with whatever material works, bubble wrap, clean dry cotton, etc. then gorilla tape the Benelli case closed and put it inside a card board shipping box. Those plastic cases Benelli’s come in are pretty rugged.
Some really good tips in this thread. Thank you.

Another option is to take it to an FFL that you trust and have them pack it and ship it. If there is one that you trust around you. Some prefer this for the simple fact that the FFL likely will be much better set ip with packing materials than the individual, and some do not want to hassle with the packing and shipping of a gun one time.

The Cameron box that I ordered a few years ago actually had 2 boxes. The internal box that contains the gun and an outer box that the inner box was shipped in. Very thick cardboard. Use both boxes when shipping.

If you don't have a hard case, I often buy the thicker pool noodles instead of bubble wrap.

If you wrap everything in paper, you can slice the noodles lengthwise and slip the barrels inside and tape them in place. You can do the same with a stock / receiver by wrapping it around the perimeter and taping in place.

The high density foam works well in suspending parts in foam when thrown around in shipping. I've used them many times in shipping heavy propeller blades without issue as well.

i use pool noodles and pipe insulation also. when i ship fragile things i crate them and then put the crate in a cardboard box surrounded by bubble wrap or foam or both. if possible i hard mount to the crate. the truth is shotguns are a fairly sturdy object to begin with using common sense care should be sufficient. i would worry more about loss , theft, or mishandling.

Mishandling is the whole reason for "O C packing" before shipping.