The shippers want you to double box it. Pack it good in one box then put that box inside a larger box surrounded by 2 inches of foam. That's what I was told. I had to ship mackie subs that way from NY to Texas weight, over a 100 lbs each.
Or you could take it to a pack and ship place like The UPS Store costs a little more but sometimes the cargo is worth the price, buy the extra ins that makes them responsible.