I would actually prefer an isolated shower stall and separate head for humidity, space, maintenance
and sanitary reasons. In addition, a "shower stall alone" becomes the de facto
wet locker, so you can use the head a number of times a day without getting wet foulies in the face.
You could also make a serious sump in there under a grate, and could rig a small washtub. Just remember to provide all ventilation to get the humidity out of the boat.
What has never made sense to me is more than one head in a boat. But then we have a Lavac