Nice! I've never seen an add-on thing like that, good idea. Only thing I would worry about is them chewing through the Sterilite... who knows though. I had quite the rat cage contraption that my father helped me set up as a little kid, I've got a picture of it somewhere... kind of rediculous and not very escape proof, but my 10 gallon tank was overcrowded too, lol. I had quite a pet rat collection... good thing they're not around to see what I do to rats now I'll post that pic if I can find it, mine was more funny than anything.