pipe thread compound, pipe thread compound😁😁 not plumbers putty. Impressed you are not afraid to venture out of your comfort zone and take on a project you are not skilled at. I am a master builder and just wanted to let you know when testing for leaks you should plug the fitting where showerhead goes so it is pressurized.
Thanks so much! 😊 We're using Kerdi Board, then a red guard type of sealant with it's matching tape for all of the seams, flashing tape and a flexible waterproof vinyl tile. And then silicone on all of the edges and openings.