Cover your backglass with a board when shipping. Use 1/8" or other thin
plywood. Do not let the board touch the glass. Make it large enough to
rest on the wood frame. Don't attach the wood with screws or tape. Use
cloth straps or large rubber bands. A backglass can be the most expensive,
difficult to find, and most fragile part of your game. Take good
care of it.
Tim Arnold pinGame journal, #25 September 1993 pp 36.