[old911doc]

Welcome to the forum!
See my post of April 7 2018.
The immobilizer box is located at the lowest point in the interior of the car -brilliant engineering decision- so water entry frequently ruins the circuit board inside and thus immobilizes the car. This problem is so common that an auto electronics repair shop in south Florida, USA, has a waterproof replacement plastic box for sale.
To access the immobilizer box, the seat above it must be removed from the car, not a difficult task.The seats are retained by bolts with E40 Torx heads, as I recall. Before you disconnect the battery negative lead to 'kill' the electrics, use the seat's electric motor to move the seat fore and aft to reveal the retaining bolt heads. Then, disconnect the battery, tilt the seat backwards to gain access to the electrics of the seat and disconnect the several multipin connectors so the seat can be lifted out. There is a plastic fastener with a #3 Phillips head that is rotated 90* to free the circuit box from the floor of the car. Disconnect the multipin connector from the box, and your box is out of your Boxster.
The immobilizer is coded to the car's engine control module and the keys, so the repair shop needs those items as well as your damaged immobilizer.
I suggest drilling a few 10mm holes in the floor at several strategic locations to allow any water that gets in to get right back out. Heresy! Drilling holes in a Porsche!
I don't know about any repair service Down Under, but ECUdoctors in the Miami area of Florida, USA provided excellent service when I had this issue. I would suggest that any newly-acquired Boxster should be fitted with their waterproof case ASAP.
Now, about drying the carpet...