Double box. pack smaller box with a lot of bubble wrap and packing peanuts. Put into larger box. Pack between boxes with lots of packing (newspapers, foam, packing peanuts,) Tape securely. Mark address clearly! Be sure to insure. If you are unsure because of size get an estimate from a reputable shipper and pass that cost on to your customer. They will not be angy with you. Their biggest concern is to have their purchase arrive in one piece (not pieces!!) I have been a dealer in glass since 1980 and have never had one piece broken in shipping.