I had to ship my Z4 back for service a few weeks ago. I was bright enough to toss out my original box, and FedEx wanted nearly $100 just to package it for me, so David came up with a great idea.
Check out local music stores and see if you can hunt down a used guitar box. Many music stores either hang onto them or just toss them out. More than likely you can get one for cheap or free. Next, put the Zendrum back into its gig bag and then use great big wads of newspaper or packing paper for filler inside the rest of the box (make sure the Zendrum isn't bouncing around when you shake the box and that there's no give in the flaps on either end). Tape up securely, and ship out.
I paid $15 for the box (got hosed, but was in a hurry and didn't want to hunt around), about $5 for filler material, and $66 for UPS freight with $2000 insurance from Chicagoland back to Atlanta. David does fast work...he had my board replaced and turned back around in 2 days.