There is a very good article, on packing a guitar for shipment, on Gruhn Guitars' Web site.

Gruhn Guitars

You'll have to explore the site to find the article.

Basically, besides detuning and packing the peghead, you must put some packing under the heel of the neck, to lift the neck off the neck rest inside the case. This lets the neck "float" and prevents damage from sudden jarring. Good violin cases are routinely made that way, as I wish guitar cases were. I even wrote to TKL about this type of construction, but I got no answer. Humph!

In addition, if you are checking the guitar, get a guitar shipping box, from your local guitar dealer, pack the case inside the box, with plenty of popcorn or crumpled newspaper, and mark it "FRAGILE", "THIS SIDE UP". That way it will survive baggage handling. Remember, the major dealers, like Gruhn, Elderly and Mandolin Bros., ship guitars, by UPS, this way all the time and never lose an instrument. I had a new guitar shipped to me, from Mandolin Bros., and it arrived in perfect condition.

EZR