Good tutorial. For me, who sends mostly slabs, I bend cardboard around the ends of the slab, wrap in bubble-wrap. Slide it into the 15" priority box and pack any open space on all four sides with newspaper, bubblewrap or whatever packing material is handy. I haven't had one broken yet. Though, it the post office works hard enough they can break anything. My broken slab collection is up to three. All received from ebay sellers:
Amazing Spider-Man 1 - Shipped in a manila envelope.
Green Lantern 76 - Shipped in a priority box that the PO absolutely crushed. Looked like it was crushed LONG ways.
Batman 232 - Priority box with no packing material. That's right, none. Just slid into the box. It rattled around in there for the whole trip.