Basically there is no economic packing method that can ensure a duckwit can't break it throwing it out the back of the truck. Crating it makes it too heavy, cardboard yields.
Best to have the buyer use one of the carriers that offers packaging.
You can make a 'pretty safe' box by strategically cutting up a car windscreen shipping box and recombining the pieces. It's getting a bit late for doing a how to but I could have a go tomorrow if you're interested.