Shipping a jet in a cardboard box is just a bad idea. A few years ago I shipped an F-86 to Florida Jets so I could fly down and pick up the plane there. I made crate out of 3/8 ply and reinforced it internally with a whole bunch of 2x2s. I think there were like 200 screws in the crate when I was done. The plane was bedded on a thick pad of foam and tied down with bungee cords. The crate weighed a ton, but when I picked it up in Orlando, the plane was fine even though there were TIRE marks and footprints all over it. You just need to make the crate tough enough to withstand the abuse it is going to get.