I bought one of these to use in the meeces Freddy 2..for something a bit different:-
I covered it in some spare lino secured with cable ties. If you do a little overlap then is kind of curls under and the can't chew it. It is quite stable freestanding, as i use it, and doesn't fall over when the cage is moved. I figured this might provide a shelving solution for bin cages..although its height will depend on the depth of the substrate as I would not recommend placing it anywhere but directly on the floor if you are using it freestanding.
I also use their rectangular wire cake cooling racks as they fit nicely in my Freddy..I cable tie them to the bars. I have them covered and uncovered and the mice seem to enjoy the different surfaces, although I haven't tested either of these with Kasala. She has a rack on its way though, when I can find time to DIY it lol.
Anyways, hope this is useful to peeps