What goes under the shower? What is correct?

and there are always many ways to Rome.

Ah, I thought while reading all the posts, and then you come up with the ending... many roads lead to Rome!
One has learned it and does the masonry, the youngest is trained on the job and makes do with methods for amateur craftsmen. In the end, a shower results. Complete sealing is important, then the installation follows - it will work out!