i would say it should be big enough if they can ball up and fit into it. i got a pot holder for a plant. (the thing that holds the extra water under the pot itself) here is a link to something like what i got. http://www.homedepot.com/prel80/HDUS...1145-Homedepot
the one i got was green and plastic, but that would work too. i just cut a hole in the top, and placed it in the cage, covered it with dirt, and put a fake cave over it, so he can have a multi level hide.
the tupperware is easy. put the lid on turn upside down, cut a hole in the side somewhere, big enough for the snake to get in and out, then put some moist someting in there, and bam! you are done. i love that potted plant water catcher things best, cause i read balls like small areas to fit into. in fact roswell only hides in that hide now when he does hide. he rejects his other hides. if i move them he will move to the potted plant one every time. plus the potted plant takes up less verticle space, and can be very easily covered in dirt. , so you wouldnt even know it was there under all the dirt.