I'm a fairly new rat owner and my boys live in a large cage with a plastic bottom. Tried lining it with fleece for a while but they just chew holes in it then land up stuck between the fleece and the plastic pan. So I just removed the fleece altogether after a few weeks. They have been living with the plastic as their floor and they have several corner layers, shelves, baskets and hammocks to climb up and down onto. I just feel like filling the entire tray with bedding turns it into a giant litter-box and they are already trained to use their litter-box which has a paper bedding in it. But watching other rat owners on youtube I'm worried I should be lining the entire cage, is it really necessary? I'm in Australia so it's pretty warm all the time and they have plenty of places to snuggle that have bunched up fabric and fleece.