It's not too dificult. There are only 2 flaps on the actual heater box and one flap on the defroster portion. There should be a piece that goes on each side of each flap. There should also be one large circle piece that goes on the top of the box where the fresh air comes in. Other than that there may be a piece that goes where the heater box and the defroster piece join together. I think thats about it. They may also include 2 pieces that go on each side of the heater core to keep heat from escaping from the sides.