It's sign making material, just like coroplast - but definately harder and not as easy to work with.
Reason why I was asking is that I know a sign shop that has "misktake" signs and this stuff is probably sitting in their trash cans .. Its closer to pvc plastic than coroplast..
It couldn't hurt to try it. I would imagine that you would have to cut the sides seperately and use duct tape or packing tape to attach them to the very bottom of the tray though. If it's harder, you may not be able to score and fold it like you can coroplast.