Just to clarify; I use paper towels for snake bedding and would toss the empty cardboard tubes in with the rats for them to chew on or play with. For some, this was totally fine, but others chewed on everything they could get their teeth in. Culling is really the only way to go to stop unwanted behavior. It kind of sucks when you get attached to a rat only to check in one morning to see her staring at you through a huge hole in the bin, but that's just the way it goes.