When a chamber is empty simply go on the corresponding turnbuckle, when you are at the top wait for your opponent to come over to you and get ready to jump. Once you jump off the turnbuckle (as soon as one foot leaves it) press forward and triangle. You should magically appear on the outside behind the crowd barricade and in the fans. You will realize if this has failed as your opponent will have hit you. You can now move in the crowd and go on the ramp. To get back in the chamber simply walk straight towards it.