Once it became clear that I was, in fact, going to be commissioned do something for AC, there was a frantic period of figuring out what that would be, and how it would be produced.
The various possibilities that were floated are too numerous to detail here (laser cut steel, massive milled urethane foam forms, etc.), but even before the general shape of the final project was agreed upon, I was collecting possible materials, and doing initial tests. Here's a bunch of Renshape and Butterboard high density urethane foam samples I got for 25 bucks from Freeman Supply. Some great stuff in here. Most of it was too hard for my purposes, but I love having this kind of thing around the shop for inspiration, if nothing else.
And here's an image of some 10 lb. sign foam I got from Sam Schartz Sign Supplies in Philadelphia. Lovely guys, and they have 2" x 4' x 8' sheets in stock. I brushed Castilene, which is a great modeling compound, onto the sign foam, and it looked like it would be a viable strategy. I spent a little time kicking myself for not having come up with this for the big lady, and moved on.