I have about 10 to 15 gerbils at any given time all in mortar tubs (plastic) and they do just fine. I love when people talk about how bad gerbils are and forget that rats can chew threw concrete. Its not about what you give them to chew threw its about what you don't give them. Make sure the tub is smooth. If they have anything to get their teeth on then its done for. If its smooth you are fine. At least thats my experience.