[DaveNP]

+1 the O rings, they're pennies from the Volvo dealer if you don't get them with the matrix.
The only issue I have with doing the matrix is it requires reaching in to the car at just above the floor of the car, I suspect it's easier if you can lift the car so the floor is about waist height, I found myself uncomfortably between crouching at the side of the car and half laying across the door cill.