Packing
Here's another idea for padding your guitar case inside the shipping box.
There is a product called Good Stuff sold at most home improvement stores. It's in an aerosol type can. It is supposed to be an insulator to spray into wall cavities and it expands to several times its original volume to fill every crevice. (Uh-oh. Did I say, "crevice"!)
I have received many personal computers that were wrapped in a green leaf bag, set on a small predeposited bed of Good Stuff, then surrounded by the foam and sealed in the box before it had time to expand out the top. After the foam expands it dries and hardens to a stiff spongy texture. It does take some practice or good judgment to not overfill the box, but even if you do you can easily remove the excess. The result was a parcel that did not shift inside under normal circumstances, and had a lot of crush protection.
Disclaimer: I can't say I've ever tried it, so I take no responsibility, but it seems like it might work to support guitar cases, too.
Guildmark