Finally i have come up with a solution to bunnies sitting in their pee! And its 100% waterproof! Built from plastic lumber (which is Unfortunately super expensive ). And a plastic coated wire mesh so its soft in bunny feet, these inserts sit down inside the litter tray and bunny sits on top. So pee and poo fall through while bun stays nice and dry on top. The standard size fits my standard hay feeders and fits inside the bottom of the van ness 11”x14” tray. The wire insert itself is 7.5”x11.5” because all litter trays slope inwards at the bottom so the bottom of the 11”x14” tray is quite a bit smaller than the top.... Likewise, the large mesh insert fits inside the bottom of the large petmate 15”x18.5” litter tray, which i use for my xl hay feeder models. The large insert dimensions are 10.75”x 14.5” because this model litter tray also slopes inwards at the bottom so the bottom dimensions are smaller than the 15”x18.5” top.