Thank you Mongo for the explanation. It came just in time. I just had two other tile guys come in today and YOU WILL NOT BELILEVE...okay you pros out there probably will believe...what I heard today. When I mentioned what the original installer said, I think David you called it laziness, Mongo you called it uneducated. Here's what I found out. I had two additional tile installers out today. I was still not hearing what I wanted to hear when I asked for details about their process, esp. regarding the moisture barriers behind the cement board and the membrane on the shower pan floor. The last guy seemed very knowledgeable and I said to myself, I've got to come on out and just point blank ask because I am not getting anywhere. He said the same thing about cement board as the previous guy, but at least HE mentioned, taping those seams of the cement board with a mesh strip and thin setting it. So far so good. I asked about some other moisture barrier for the framing before cement board. He said they use a poly liner thing behind the cement board on the exterior wall. They don't normally do it on any other wall but they could... no problem. He mentioned some of the new boards that are lighter and made of foam, but he said they don't use them. Same deal, unproven and he would prefer cement in his own home. We talked about the shower pan membrane and he too talked about sand mix, membrane, build slope and tile. I finally came out and said, "I read somewhere the membrane should be put on a slope or something." He said we generally do it flat but what you are talking about is the pre-slope. He KNEW ALL ABOUT IT! What he said next floored me. He said yes in the Highland Park area we do a preslope. They have million dollar homes there. Not to say your house is not nice, but that area has more restrictions. Mongo, David and Bill...he described the steps just like you said...I guess my less than million dollar house didn't warrant the "correct" installation technique. :-( He even said why it is better to put it on the preslope, but I guess "cheap" houses don't get the extra steps. LOL I asked him about the membrane placement and he described what I had seen in the Harry Dunbar website. He did say he goes up about 8" on the walls, not 12 inches. He did say doing the preslope would make the shower pan area higher, but I told him I did not have a problem with that as long as the membrane was on the preslope. He did not have any problem doing it, but I am sure it will be reflected in the estimate he gives me. :-( Thought you guys would be interested in what I found out today. Thank you so much. I definitely will not be using the first guy.

Corian, Swanstone, Kohler Choreoraph, and Transolid are all covered in this thread. We have been talking about solid surface showers here for years. You can search the forum by using the search function at the top of the page. My 37 x 63 Transolid shower cost under $4000 and that included a sheet of the material to cover the ceiling with and the shower pan. [Here is the thread on solid surfaces that is most recent.[(https://www.houzz.com/discussions/kohler-choreograph-dsvw-vd~3420698?n=216) I think that the Corian, Choreograph and Swanstone showers I have seen pictures of look the best. Not as shiny as quartz, but nice. And a multitude of color and pattern choices with Swanstone or Corian. Someone posted recently, though, that they can't find Corian showers any longer. Don't know if that is true.

sheepdog55, I think they do make them now at a 96 inch height. I think at the time we ordered, there was a major delay in manufacturing or something. We looked at a few different Swanstone vendors and could only get the 72 inch height in the specified color and size. You might have luck finding the taller height now. I absolutely understand what you are saying about minimizing vs. eliminating grout lines. As you can see, we have quite a few grout lines in our accent tile. However, our old shower was the same height as where the Swanstone hits so we figure the accent tile isn't really a big gamble in water damage, especially considering the waterproofing measures we took. It sounds like your idea would be lovely!

It looks like you want a tub that is wider, longer and possibly deeper than your current one. There is a good chance that you will need a larger conventional water heater or an on-demand water heater to fill it properly. If you use a pocket door anywhere, be sure it is a solid core door to reduce sound transfer. If this were my bathroom, I'd remove the closet but leave a partition wall against which the door would open. Then I'd move the toilet far enough toward that wall to put a new tub roughly where the current one is. I'd put any money saved on extensive channeling toward a Toto Neorest toilet.