I have found that, depending in what size of knife your shipping, Cardboard tubes work very well. I simply roll up the knife in a bit of bubble wrap, slid it in the tube, and stuff paper in ends, or more bubble wrap, and tape it up with water proof packing tape. I always make sure to tape the whole package, every inch, to ensure nothing unintentional gets in or out. Tubes come in many diameters and cloth stores are a good place to get the thick industrial strength ones, and they are free!!!