I’m running my trusty old Antec 900 with three Rosewill hotswap bays to hold 12 3.5” drives.
https://www.newegg.com/rosewill-rsv-sata-cage-34-hard-disk-drive-cage/p/N82E16816132037
I’ve got this laying on its side currently, and I need to replace the failed top exhaust fan, but I’m sure you could come up with a rack mount option to throw it in a rack. Probably about 4u tall on its side.