Wet Trunk

Every time I drive in the rain my trunk (and everything in it) ends up soaked. From reading pervious threads I learned a bit about drains, damp floorboards and trunks, but after checking the drains in the sunroof and the seals around the taillights (all was fine), I don't know where else to look. The body is solid and there are no leaks evident after taking all of the trunk padding/carpet out.

Also, while having the head gasket replaced and the battery changed my mechanic told me that the battery compartment under the rear seat had some water in it so obviously the leak is affecting the battery compartment as well.

Thanks and any advice is appreciated.