We started using the storage boxes as well; they are about 2' high so we just cut holes about 5" up for the cats to get in and out of. This makes it a bit more difficult to fling the litter out of the box! I've also got one who for some reason would pee over the top of a standard litter box, so this keeps everything contained. The walls are high enough that I don't need a cover for them, which the cats like.

We got ours for about $4 each at BigLots. Works much better than the $20 ones at Petsmart. I highly recommend these!