I just booked a handicapped room on a RCI ship and HAD to send a doctor's note to my TA so they could send it to the ship. My mom happens to have arthritis real bad, plus other ailments. She can walk but still needs a wheelchair because she tires so easily. I also had to send a letter from the doctor to the cruiseline stating she will be bringing needles on board.
Haven't been on the RCI, but I hope you don't book just because of that.