I kept pet rats in similar cages with plastic bottoms for years and never had any issue with chewing out. Finally after a long while one did start to nibble but she was a notorious chewer. If they have enough other things to do, stuff to chew on, and things to mess about with, as well as not being overcrowded, most won't bother to chew on their enclosure bottom (at least in my experience). Those look like lovely multi-level cages for a couple of pet rats.