Made two of these bins and have a few notes in case anyone else wants to try this...

Cutting hardware cloth leaves very sharp edges. I cut in the center of each square and used pliers to fold down the cut edge toward the center of the piece. Tried sanding with a Dremel but the vibration often tore apart the cloth's weak construction and I was left with free wires.

I wanted to use nuts, bolts, and washers to mount hardware cloth but couldn't find any of decent size in time (either too big or too small). Mounted with black zip ties and so far the rats have zero interest in testing these with their teeth. I mounted the hardware cloth on the inside with 1 inch overlap on all edges to prevent chewing. The two long sides are cut out with an intact lid, since I intend to stack them. Also, the term "hardware cloth" is a lie since there is nothing soft or gentle about that stuff. My poor fingers...

Right now there are water bottles hooked onto the sides but I might move to a gravity system. Two mommas with fuzzy litters are in one bin and they through an entire bottle in one day. Interestingly the rats' behavior has changed. They are much friendlier and less prone to charging the cloth when my fingers are near, and aren't as aggressive in defending their pups. Wish I did this sooner!