I am the opposite of Suzy Lee - I have had great success with #6 Plastic!
#6 is the kind that clear boxes from the deli/bakery are made of btw. So easy to find and cheap to use. Cut out the flat section of the box, rough up one side with sandpaper, then draw and color on the rough side, cut out and bake @ 300'F. It will shrivel up and flatten out just like shrink paper.
But one down side is every plastic container is a bit different from the last, so some times you will get a bad one, and it wont turn out just right, but don't worry, it's not you'r fault, lol.
I would recommend trying the #6 plastic before ordering online, you might find that it works really well for what you needed, and you wont need to order anything :)