I am building a steam shower an have had to sort through a lot of conflicting information on the web. I know many like kerdi or nobleseal but the inside membranes seem like extra cost, more pieces or strips to leak and more work to install (two layers of thinset). I am looking for feedback on my current plan.

I have an acrylic base and ceiling that are preformed and steam compatible so For the walls I am planning..

2x4 stud walls

pvc or cpe membrane over the 2x4 will go inside the lip of the acrylic ceiling and base sealed to the lip top and bottom

1/2 inch durock over the cpe or pvc membrane

unfortified thinset joints mid wall, but silicone joints between wall panels and between walls and ceiling /base to allow for expansion.

unfortified thinset and grout to adhere my tile with white silicone at ceiling/base and wall junction to allow for expansion.

Based on what I have read having the vapor/moisture barrier outside the enclosure is ok as long as the thinset and grout are not latex modified as this would trap moisture beneath the tile.

Thank you