What I generally do when traveling from International destinations, is to get the box covered in plastic. There are counters in most of the airports outside the US where they wrap your luggage in plastic for a small fee. I feel more comfortable when I do this.
I have taken Cardboard boxes from US to India on a couple of occasions without any wrap and it came thru without any major damage. Also, we do not put any sensitive stuff in the boxes. Any thing sensitive / anything that might come up in an X ray generally goes into the suitcases.
