I just packed up and shipped a 12" sunfire sub. those subs are notoriously difficult to ship, and have arrive, undamaged.
I had to custom make the packaging, over time, as I thought about how to go about it.
When I was done, I had a 55lb box that could be stood on, on any side, and more.. and even bounced down a set of stairs. Which is how an item should be packed, if one is going to try and ship it via UPS or FED-EX or USPS.