1. Get a lot of THICK foam padding - the stuff you put on your bed with the curved depressions. Pack into the cavity *underneath* the harp snuggly, and then on top of the harp (tone bars). Then put the harp cover back on so it is nice and secure.
2. Put padding on top of the keys and then put the cover on.
3. Use packing bubble tape and wrap the entire piano being sure to cover the latches and ALL EIGHT  corners  in your rotation. Go around at least 4 times.
4. Get cardboard (old broken down boxes, etc.) and tape it onto the piano, being sure to cover all the areas of the tolex, and then cut out slots so all the handles show through. You don't need to find a box per se that will fit the piano, all you need is scrap sheets of cardboard to create a "shell" around the unit. The thicker the better.
5. Write FRAGILE all over the box. (maybe this will means something to shipper company, and it gives you peace of mind).

(thanks to John Della Vecchia)