Using QR skewers to keep the pvc fork and frame spacers in place is not a good idea. That will create "points" that can easily punch through the shiping carton.

An easier plan is to go to virtually any LBS ans ask for ALL of the packing gizmos that new bikes are packed in. They will include a little plastic thingie to put between the fork blades, a pair of mushroom thingies to put over the rear axle, and another mushroom for the front hub axle. I've worked in several shops and we always just gave that stuff to anybody who asked.

While you're there, ask if they will let you look into box containing a factory packed bike. Another thing to consider is not all bike boxes are the same size. Road bike boxes tend to be a little taller than mountain bike boxes.