They're so cute! My sister has a rat too, and he is so gentle and loving - he will lick your hands when you take him I love him
Your rats have a large home I wonder if you ever tried letting them run/hide in the wood chippings? All rodents love any paper or wood chippings - they love to play and sleep in them. Try this with your rats - they'll love it. And it is much more comfortable than metal crates.