I wonder if it might be worthwhile to investigate using the services of a fine art /antiquities specialty shipper. They aren't cheap, but they are careful and they know how to handle fragle/delicate/valuable cargo. Fine Art shippers aren't available to all parts of the country and you ship on their scheduled runs to a given geopgraphic locale, so you have to wait a bit longer for service. Try someone like shippingmadesimple.com (Transport Consultants International.)