I have keep gerbils for a while and always used to keep them. I had a group of 4 in a tank (I am not sure what size but I believe it was a 100 gallon) when I was younger. I then moved and took in a rescue group of 3 very much on the spur of the moment. Two of the group passed quite quickly and so Starscream was moved into this cage
(this is not him in it though)
He lived to the ripe old of 5 and then I took on three more with the idea of getting my large aquarium back from my parents loft. Sadly Carbuncle passed quite quickly he had internal problems and Serket followed quickly. I believe it was a genetic fault but not know the history I can't confirm that so now Odin lives here alone.
I know a lot of people will say no to tank topper but I find that the best thing about them is that they allow for a very good level of interaction. I couldn't interact with Odin in his tank as it is a maze of tunnels and substrate. But he will come up to the tank topper and interact with me of his own choice.