I ship my shotguns by USPS, registered mail, insured. They require the outside box to be cardboard. They require me to use a brown paper tape to cover all seams of the box. USPS sells the tape, as do office supply houses. It is water activated. I cut the tape to length and then put it on a plastic counter top and wipe it down with a wet paper towel and then stick it on. Significant learning curve and time involved in the first time shipment. After that it was a lot easier.
For me the only thing worse than shipping it USPS is shipping it some other way.
