My aunt said that the target caddy had a bar that went under the edge of the mattress. We weren't sure how a little rod would help hold up the bed caddy loaded with books. She came up with the idea to use a non-slip rug pad to tuck between the mattress and whatever that mattress rested on.
I added a couple strips of ribbon on the top and bottom edge of the non-slip rug pad to keep the connection to the caddy from ripping. I think they turned out really nice. Pockets for Pens, a phone, the all important book, and even an Ipod. Who could ask for anything more?