I wanted to get mesh grids, but I still haven't found a store that sells them around my area.
I could always buy online I guess, but it cost way too much that way.
But your right, it does hold in their litter a lot better and you can even lower the coroplast walls to give them a better chance to see what's going on around them.
Nice verticle hay rack. I made one myself, it's actually posted in the hay rack section in the photo gallery.
If you really wanted to get cavy crazy, you could add a second level to it with a ramp. It's not that hard to do, the only tricky part is making the ramp.
Other than that, nice cage, set up, and keep up the good work!
~Chris S.