http://www.homedepot.com/p/HDX-36-in...8974/100006678
This style with the shelves deep enough we could slide a 54-qt Hefty tub in between the supports on the short side of the shelf, it may even have been this particular model. We used a hacksaw to cut the plastic support posts so that the underside of the shelf above the tub keeps the tub lid secure while still permitting the tub to slide in and out easily. Also the holes in the shelf allow air under the heat tape so it doesn't overheat, since the acrylic sheet is on top of the tape this was a concern.
We used two shelving units to create one six-tub rack and one two-tub quarantine rack. The downside to this rack style is the open sides. For the six level rack it didn't matter since it's in the snake room which is kept fairly warm compared to the rest of the house in the winter. I had to cover the QT rack with a blanket and put a hide over the heat tape, and then it stayed warm enough for the slithers.