Designing Kitchens and Bathrooms - Tiling a shower with bench

I have installed a bench in my shower and am wondering the best way to prepare this area for tiling. I am planning on installing the backer board to the face-portion of the bench and floor mortar for the top-portion of the bench. I don't want to put screws through the CPE membrane, at least the top portion. Is this the best way to do this?

You cannot do the bench the way you propose with cpe membrane. If its already there, remove it. Treat the front of the seat as you would the other walls, that is run the cpe membrane up the front of the bench 3" or so above the curb height, and then cement board, no screws through the membrane. Use 3/4" plywood for the seat, then cement board over that. Use a surface applied paint on membrane like redgard over the top and front of the bench, extend the membrane 5" or 6" onto the walls where the bench meets the walls.