Water leak in boot

I have had an issue for the last 6 months that continues with water leaking in the boot from somewhere, the water is not massive amounts but it is looking behind the second skin near the rear lights and the cars outer skin. There is a hole in the inner skin that you can put your hand through and touch the floor where the water has pooled and you can pull out a rubber bung that must be for wires so you can let the small amount of water out. Also near this but is some sort of vent that goes to the outset skin where the rear wheel arch is so could it be leaking from here? 

I have read that water can leak from the rubber gromits at the top of the boot where the boot wires go from the car to the lid for the lights electrics but the rubber seems ok.

We have stripped the boot out with the trim and carpet but because of that inner metal skin you can’t see the water or where it could come in but we can’t figure it out so would appreciate if someone could really help me with this. As I can’t use my boot and it’s all apart and look nasty at the moment and also don’t want the water to cause more problems. I can provide some pictures of the area I’m on about if you don’t know where I’m talking.

please can someone help me, lady in need of someone that knows what they are talking about

here are the images below 

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