One of my quarantine enclosures is a single tub 'rack'. I really like having a single level enclosure because it's easy to move and is convenient.
It's basically a box built around the tub(28qts). The heat(6 inch THG heat tape) is in the back and the tub slides out like a normal rack would.
Mine is made from 1/2 inch wood, but PVC would be really nice.