I can see the point if the car was damaged by flood water , then the insurance would be liable . But if it is caused by normal rain water penetration , I can see why it was rejected. Big bill at best of time , never mind Xmas .
A problem with all the boxsters as far as I know. there is a drain hole at the nearside under the roof panel (you can get to it by half lifting the roof0 this should be open to allow water to drain down under the car.
if not it will hold water and eventually run down the back of the NSF seat and soak the immobiliser unit and possible blow the engine management unit.
You can clean them out with an air hose from your local garage or a piece of welding wire.