The last double I shipped was in a hard takedown case. I don't know what some have against peanuts but I filled all open spaces around the gun with them. I then constructed a heavy cardboard box myself to enclose the case. I shipped it USPS Priority with $201* insurance and signature required.
*All of my collectible firearms are insured with CIA so I just needed the minimum postal insurance for tracking and signature to meet their shipping requirements.
jim

The 2nd Amendment IS an unalienable right.