Phoenixx, I work for the Post Office, so I will try to answer this one for you.
If you have the original box that your humidor was shipped in, that should protect it. If you pack the cigars inside so that they will not shake around that should be fine to. If you don't have that box, or are going to place that box in a larger one, wrap it with a towel, or sheet, tape that in place, and tha will protect it. Other wise pack it into a box again protected with a towel, sheet, or other cardboard wrapped around it.
Remember if you cannot drop it 3 feet safely, do not ship it. Stuff does get dropped, and stuff does get shaken up, and I don't think there is a shipper alive that will allow for breakage.
If you have any more questions, don't hesitate to PM me. If I can help, I will.
Good Luck with your studies!