I actually used one of those containers for protein shakes. They're made of some pretty good plastic.
My roomate is kind of a health freak so I took one of the containers for his protein and cut it in half. Makes a great hide and the BP loves them. That and they come out identical.
Here's an older pic. I have since added some more vines along the back to make it look better
http://www.ball-pythons.net/gallery/...7/9/7/3/04.jpg