I bought a set of 906's from someone many years ago that were shipped to me in 2 separate wooden boxes that were made out of 2x6's that tightly surrounded the head and capped top and bottom with 1/2" plywood. The heads are about 45lbs each and the first trip the boxes got banged up a bit. I fixed the damage, added a little more reinforcement to keep the heads locked in place and have since shipped heads in them multiple times.

I ship them either UPS or FED ex and insure them well, the high value gets them a little better care in transit.