[floatingkiwi]

Hi all
I posted on this last year (aeons ago) as well.
I found that the seals around the lights (inside the trunk) were causing the moisture problem also compounded with a slight deformity-from-manufacture that was causing the metal to bow inwards a bit much. ALSO you may find that the plastic plugs in the panels below the rear lights (also inside) may also be leaking.

I sealed both items up with a little bit of silicon and hey presto, no more moisture.

Matt