I appreciate your input but rabbits can do very well on wire flooring. Though there are exceptions for certain breeds and individual rabbits. My rabbit enclosure layout comes from breeders who've been keeping generations of happy and healthy rabbits on wire flooring for decades. Rabbits that are $200-300 each so they care very much for their rabbits' health and well-being. Many species also thrive down to -40 degrees without any heat source so warmth isn't really an issue for outside rabbits. Adequate protection from elements is necessary of course, especially wind and rain.
It's certainly debatable but I think constant fresh outside air and sunshine, in addition to cage objects for interaction, is far more healthful and enriching for rats than being inside a cement tub inside a rack inside a building. Nothing wrong with the tub and rack though either... that's what I'm using now.
I too am having a hard time seeing how rats could be safely kept on a mesh floor large enough to pass their excrement (we do agree here) but that doesn't mean someone hasn't come up with a system that works and keeps them happy and healthy too. I'm hoping someone has and could share their method.