I have the valves, but I haven't yet ordered the trim, and I wasn't planning on getting it until the tile is in. I also have all of the PEX and shark/gator bite fittings that I'll need. As you can tell from the picture, I'm dealing with a rather oddly framed wall where the plumbing will be. It's original (100 yr old) true 2x4 framing with new 2x4 framing laid flat against it (to save space). I'll have to carve a little bit of foam out of the insulated wall to fit the valves in, and add some cross supports to mount them to. My concern at this point I'm sure is very basic, but here it is: How do I ensure that the valves are mounted at the correct depth? I can't put in cross supports until I know exactly how deep they need to be, and I have to take into account the 1/2" hardie backer and the thickness of the tile. Any advice is appreciated.