When i sent the 10" away to get recoated i was advised to just pack it in a strong cardboard box wrapped in foam. Didn't like the idea, Aus post could break an anvil. Made a 12mm plywood box 25mm bigger all round than the mirror, rested it on its back on 12mm dense foam, covered the business side with tissue and more 12mm foam on top, with strips of foam around the sides to stop movement. then screwed the lid down and struck lots of FRAGILE stickers over it. Survived the two way trip nicely
Bill