I just made contact with a company for packaging supplies. www.sannahpackagingsupplies.com
They have all the necessary materials to help you ship your works. I used a product called Instapak RT (room temperature). They are polyurethane bags that contain two chemicals that you mix together by kneading the bag. The resulting reaction makes polyurethane foam that fills the bag quickly. Once the reaction is started, you put the bag in the box and place your sculpture on top the bag. It forms around the bottom half contours of the piece and cradles it. You do the same with the top of the piece. The bags come in different volumes. The reaction is exothermic so it produces heat and steam that vents through minute holes in the top of the bag. What I found is that if you wear gloves you can form the foam as it expands. Making a protective cocoon for your piece that you can use every time you ship that piece. In this case, to nest the sculpture in shipping both to and from the exhibit.They have taken a commercial process and made it DIY. The price is very reasonable from them.