Efiwym and I have talked for years that we wanted to replace the fiberglass shower in our master bathroom. The fiberglass had discolored and was coated with a soap buildup. Three times I needed to repair a leaky floor drain.
I could access the underside of the shower from the inside of the kitchen cabinet below. We had a dropped soffit above the cabinet where the drain was located. First, I removed all the dishes and supported the cabinet with wood blocks between the counter and the bottom of the cabinet. I was able to sit in the cabinet while I twisted my body to remove the drywall and get at the drain. Once I removed the drywall, I checked the drain for leaks. I tightened down the drain nut and it apparently took care of the problem (for now).