I've shipped at least 200 guitars and I never loosen the strings and don't put anything to protect the frets. Never had a problem or a complaint. But I would definitely explain to any buyer that the guitar was going to be shipped sans strings, thats just werid IMO? 1st thing we all do when a guitar arrives is see how well the setup is, then restring if necessary etc
If you buy a brand new Gibson guitar it comes in tune and with nothing protecting the frets from the strings so I have no idea who came up with the idea of loosening strings is safer?
+1Worry is just a dividend paid to disaster before it is due.
Wait till it gets there then let us know if there's a problem. Until then sleep easy.
If it comes with the neck off I'd call that a kit, I bought a whole guitar. Strats with neck off can be troublesome they don't always just reassemble and play right, might of had a shim thats gone now or the saddle screws could have turned w/no string tension on em?