waterproofing shower nook

I am going to be tiling my moms shower. I bought a plastic shower pan and am going to be using dens shield for the backer. I am going to be using redgaurd on the seams and screw heads to waterproof it. She would like a nook in it to put shampoo and stuff. Can I just frame this out and use dens shield and then redgaurd to waterproof it? Is there some kind of tape I need to use on the seams with redgaurd, like fiberglass tape? Would I use tape on the outside corners where the nook meets the shower walls? Thanks for any advice with this!