After heavy rains my 2003

Hi.
There is no drain plug. The leak is usually from the convertible top where the window meets the top. The water drips down the window flooding the floor board. Often you do not notice water because this is slowly leaking through the passenger door surface. In that case the problem is window seal, and repair is not expensive.
The only other possible leak inside the car is from rooftop, but in that case you usually notice damage, and the leak does not pass unnoticed.
Regards.