I've heard people say you should get a dig box if you don't use substrate (which I'm not planning to). Would a cardboard box work? This is what I have prepared for when I get my boys, its filled with shredded paper, balls if news paper, toilet roll tubes, and pieces of cardboard (I will also scatter some food in it when I have my boys). I'll probably change it when I fully clean their cage weekly, and replace it with a new one. Opinions?