I want to build a shower pan using Hardibacker board and Redgaurd.

I will simply be using Redgaurd as the liner under the the Hardi Backer, which will be screwed down to the plywood, using the mastic as a base to create the 1/4" slope, then painting the top of the Hardiback with Redgaurd. I am also planing on using 2 layers of hardiback as the substrate for the Tile.

I will coat the hardiback with Redgaurd then tile directly over that using mastic and tile. Is this a sufficient and safe way to build a shower base?