To be extremely safe I would suggest doubling up on the insulation and adding your heat packs. Set a test box outside for a while with a thermometer that records high and low. I am sure the seasoned reptile breeders have something to add to this but it's what I would do

It's more then just your temps. The temps where it's going, as well as the temps where it will sit overnight in a warehouse need to be considered as well. Heat packs sometimes fail as well, another thing to consider.

That being said, it's a Colubrid, and they've been known to handle pretty low temps better then a lot species. (that's not a suggestion to ship it BTW, just saying)

Is this a genuine question? You're in Georgia, but you're moving your corn snake from Alaska to South Carolina and the temps are below freezing, and you ask the question in a thread about how to get certified with fedex?

IF it's a real question, which would be really weird and I'd love to hear the story behind it :), don't ship it. Wait til the temps are better. The temp spread between Alaska and SC is too great, and to heat the package properly for Alaska might just make it too hot for SC... since it's not averaging 20F there, even probably at night. But the package would arrive during the day when it's almost certainly much warmer than the temps you've given.

Is this information up to date?

I don't know of anything that has changed except that I can only drop off my packages at a fedex hub. Mine is 45 minutes one way, but the last drop off is at 8 pm so I don't mind so much. It just means my geckos spend less time in transit.