Thanks everybody! I'm glad you all liked it
So far there's not been a problem with destruction. I was surprised but the 3 boys have had their set-up for a couple of weeks and they've not taken one nibble at the cardboard levels. They only chew what's down inside their tank, like the tissue box they sleep in. As for the girls, they're determined chewers and they both chew on the metal constantly but I guess because it's powder-coated steel they haven't even been able to scratch it!