We have two gerbils and they love to chew and shred things. This is fine. That's what gerbils do. We like to give them lots of different things to much on as a change from card board loo roll centres and egg boxes.
My local cheapie store has straw bird nesting boxes which are just straw woven together and secured with string. Spike to attach them to a tree which is easily removed. And they're only 99p which is way cheaper than proper gerbil houses!
Any reason that we can't put one of these in their tank and see how they get on? If they don't chew it, it would make a nice cosy wee house for them.