Another option if you like....cover the entire bottom with linolium or stick on tile squares. Both can be bought rather inexpensively at places like Home Depot or Lowe's. That's what I cover all the floors of my ferret cages with. I also LOVE Martin's cages. Of course, I've never owned rats so I'm not sure if they'd try to nibble that so i'm not sure if it would be a good option...but just an idea that I thought I'd toss your way.