Do you live in an area that gets low in temps? That would be an issue for the rats, they would get URIs. Which is, of course, no good. Rats definitely don't thrive in the cold, or really hot, temps. I assume you probably know that already, though.
Perhaps it could be possible if there was an abundance of soft hammocks and hides in the cage, and maybe a shelf with a solid ground, that way they wouldn't be forced to be on the mesh all the time. If I noticed they felt more inclined to sit on the mesh, I would go back to the rack system. No point in risking pain and discomfort when there's already a system that works.![]()