I agree with using pvc/abs pipe. You can make your own box or use the Priority box. I think you save on the Priority box.

On a related subject, I started shipping my guns out for service using an inexpensive aluminum gun case from Ziegel Engineering, in its original cardboard box. I feel pretty comfortable they are as protected as I can make them. Wonko turned me on to them. Ziegel is minutes away from my work in Long Beach CA.
http://www.ziegeleng.com/pg5.htm