HI, Some boxster owners also had water under the carpet because of 2 drain holes being blocked, located on each side underneath the retractable panel of the convertible top , so verify those holes by pouring water into them and it should come out underneath the car.
Do a search and i think someone had posted pictures of where all the drain holes are situated in the Boxster.
Also on the passenger side is located the air conditioning drain hose, make sure it is draining beneath the car and not under the carpet.
Good Luck
