Get two, or even three of those, and paste them together, caulk the seams, only put the back on the last one. That'll give you some more depth to work with. 11.5" depth isn't very much, but 23" isn't bad, and 34.5" would be quite nice. Not saying you can't do it with just one of those, just saying that you will sorely lust for more depth if all you have is 11.5".