I have shipped and received more bows than I can count, and in some cases even PVC was not enough. In one case I sent two bows to John Strunk in a PVC tube, and when it arrived at his house about 12" of one end was missing. I have also received bows with 5" or 6" of the limb sticking out the end cap. I sent a bow to JD Jones once and the entire mid section of the tube was shattered. PVC is brittle, unless we are talking about a 2" 40, but that would have to be a very straight bow.
Heavy cardboard tubes, like carpet tubes, with wadded paper at the ends has never failed to hold up.