I did a lot of research on shipping large artworks safely and found several great resources. One great site with a ton of info is encausticshippingiea.wordpress.com
They speak mainly to shipping encaustic work but the techniques would definitely work for almost any kind of 2D artwork. They also provide a resources section where you can find many of the materials needed. I used their tutorials on building an insulated shipping crate and shipping box. Below are several pictures of the process.