I am in the process of installing a bathroom in my new garage addition, and am seeking input for the 36" Sterling shower enclosure.
1) Instruction state that back and side walls can be attached to bare studs or over water resistant wall board. Any opinions on which is best?
2) The base I plan to put directly on the cement floor. Instructions state that if base is installed on subfloor other than plywood, spun polyester landscape fabric can be placed under the base to prevent squeaking. I am thinking of applying expanding foam at the edges of the base for added support. Any problem with that?
3) The 2" drain comes out of the floor. The trap is in the slab. I bought an Oatey ABS shower base drain that enters the base from the top and is secured with a nut from the bottom of the base. To accommodate the nut, I would have to chisel a 4 1/2" dia x 1" deep around the drain pipe or put a 1" plywood subfloor with a 4 1/2" hole under it (that I would rather not do). Since the drain would be attached to the base, gluing the dain to the 2" pipe could be a pain, as the ABS glue dries rather quickly, I would only have one shot at properly setting the base on the drain. Do they make a drain receptor with female threads on the inside that could be glued to the 2" pipe afer the base is set, and with the drain grate screwing into that?

I thank you in advance for any learned opinions