What are you saying about our fair country? it's always fab convertable weather here, lol.
Have you taken the carpets out? normally it's the drains but it could be a hole drilled by a previous owner or damage for example. Does water flow through freely when you use a hosepipe down the drains?
https://sites.google.com/site/mikefocke2/drainsdiagram
You want to sort this before it destroys the expensive bits under the seat. As mentioned earlier, try taking out the seats and lift the carpet and get someone to use a hose pipe and see where it's leaking from if the drains are definitely clear.
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