[Andy Friar]

Double wall boxes and using hard insulation foam and/or a double wall box with an inner cardboard box and a few cans of 'great stuff' spray foam between the layers. As UPS plays rugby and/or chucks the box around, the heavy item sliding around inside has more often been what causes the box to fail in my experience. Good fiber tape is a min recommendation as well. While I worked for 10yrs as a design engineer and then prod/quality mgr for a Harley transmission aftermarket company, I had to design packaging and source boxes. UPS would pay out on the insurance, but ONLY if you had it packaged amazing and meeting their high standards for shipping. Just remember you care about those heads more than anyone else. CYA and package them in separate boxes to drop from above your head and have no damage.