The situation resolved itself because they decided to move out, and as a precaution I took up the new flooring, installed a vapor barrier, and installed new flooring on top (painful since I had installed it all a year before, but in the end it really just came out to a few months profit).

Once inside the walls it can simply sheet down the voids on the backside vapor barrier.

Water is now so hot they must be having a steam bath inside the bathroom & I found that the chrome coated shower rod started to rust from so much residual water vapor.

I use a vapor oxidizing system for MH's and rentals to remove smoke smells. 

Plumber recently went down to crawl space to inspect and told resident there needs to be a vapor barrier.

Hello BiggerPockets Community,I'm embarking on an exciting journey to acquire and renovate a duplex from 1900, aiming to tackle the inherent challenges of outdated insulation and the lack of modern vapor and air barriers.

This ^^^ Or just build the little wall and stand it up in place...attach to ceiling and floor, apply vapor barrier and then cement board.

Also need one for retiling bathroom (vapor barrier and cement board).

I also don't see any vapor barrier in your detail.

I'm sure this would negate the need for a vapor barrier?