welcome here! i prefer using cat litterboxes, the medium size (about 12×16 inches) over the corner critter boxes. this gives plenty of room for doing their business, lounging, and munching on some hay! not only are they half the price generally, but they have higher, thicker sides, so that might help with your chewing (and kicking litter out) problem. to attach it to the side of the cage, you can drill one hole in the side, about one inch from the top. loop a ziptie thru it loosely, then attach to the side using a dogclip.
that’s what i use to secure my hay box to the side of the cage. here’s a pic. you’ll see on the far left of the pic there’s a black ziptie, and all the way out of the pic, there is a little glint of gold. that’s the gold dogclip that i use to secure. it’s great because you can easily take it apart when it’s time to clean, but the buns can’t budge it.

on either side of them are their two medium cat boxes…
edited: those are my babies by the way, Max the lop and Meadow the mini rex… lol.