Ouch!
in the mean time though, you need to find out WHY the immobilizer got wet. Unless you left the car or window open during a downpour, you need to find out why there is water under the driver's seat to begin with. Most likely culprit are clogged drains in the soft top reservoir or a tear in the cavity's apron.
Detials on Drain Cleaning Here from Mike Focke's Boxster Page
