Mike,
This seems weird. I checked the 98, 99,00 and 01 Contessa Naples and all have the plumbing access door. It's on the driver's side just behind the slide and just above the belt-line. It's about 4"x7" and has a locking handle. If your shower is not located on that wall (e.g the 38' San Marcos) the door is not there.
Steve