In lieu of a bag, wrapping it in Saran Wrap works well too. You just want to isolate it from newsprint as ink will rub on the leather. Bad thing.
Wrap in Saran Wrap (or a bag), fill the bottom of the box 1/3 full of crumpled paper, put the saddle in, continue to fill the box. Be sure the saddle is centered in the box. Use just enough paper so that you have to put a TAD of pressure on the box flaps to seal it. That will ensure nothing moves around inside.