I have two girls I'm going to get a bigger cage for but the cage I found doesn't have a very deep bottom. I was wondering if anyone here with pet rats (and I know there are plenty here) have had any success with litter training their pet rats? And what are your cage preferences? I was looking at the Critter Nation Rat Chinchilla Squirrel Cage Midwest 161 BUT the tray at the bottom looks very shallow.