Doing an upstairs new bathroom, eventually with a (fiberglass) shower base. Currently has the plywood subfloor down and all the plumbing roughed in. I can't get a straight answer between my plumber and the guy who's doing the floor tile about which should go in first. Both have an "you can do whichever you want" attitude, without telling me which is best for creating a water barrier. The bathroom is directly above the first floor master bedroom and I don't want any water seeping through. As far as I can tell, there's three options:
1) Install shower on subfloor. Run cement board and floor tile right up to it and caulk. (I think this is the worst and will definitely leak.)
2) Install the cement board all the way under the shower, then install the base, then run the floor tile right up to the base. (I think this is probably the right way, but I think my tile guy isn't happy about making two trips and waiting for the plumber in between.)
3) Install the cement board and floor tile under the shower base. (I think this is overkill and the tile guy said he's never done it that way, but it sure is better than Option 1.)
What's the right way to go here?