Colin:
One way to protect it is to avoid using UPS... but that's another story!
Fisher Jones' suggestion is a good one but a little expensive. I think you can do the same thing yourself considerably cheaper by:
Obtaining - a cardboard box larger in all directions than the top -many large plastic bags of various sizes -some spray cans of polmeric disocynanate - resin - gas mixture (high expansion foam).
Then place the top in the box and block it temporarily in place while you spray foam into plastic bags positioned to support it in all crucial areas-the foam inside the bags will expand to fit the box and the top and can also be molded or cut later if desired.Then do the same on all sides and corners and you have a light strong package that will generally take most of the abuse any package labelled "fragile" or "this side up" usually seems to get!
Some commercial insulators may also do this for you with a similar foam, and VB ships its windshields this way
Hope this helps!
Ron Tebo