I have shipped a couple of vises, not quite that heavy but still pretty stout.
As I was shipping via USPS Parcel Post, I started by finding a box to fit the vise, cut a base from a piece of wood, bolted the vise to the wood and then add the sides to create a wood box that fit inside the cardboard box. If you are shipping motor freight, you would do the same except for the cardboard.
I have some pics at home of some of them I can post later. Box it and brace it well to allow for the worst possible handling.
Brian L.