Schluter Products offer a full line of tile installation products including this easy to install shampoo niche. The unit comes waterproof and ready to install. Fits anywhere with a 16″ space which is industry standard for framing. More info can be found at www.Schluter.com.
You can also add an additional layer of water protection using Epoxy Bond™ with sanded cement based grout such as Polyblend found at Home Depot or Mapie Keracolor at Lowes.
More info on Epoxy Bond™
TheGroutStore – official supplier of Epoxy Bond and ceramictilepro products
YouTube – officially supported how to videos using Epoxy Bond and Grout Bond products by TheGroutStore.com
Amazon – original genuine grout repair products manufactured by TheGroutStore