I've completely sound deadened the car. Roof (no more rain noise like you in a dustbin), floor, boot, inside doors, rear quarters, b pillar and even the boot lid. I bought a strip of weather seal expanding foam from screwfix and stick it on the bootlid so it squeezes between the boot rubber and boot lid .
sticky pads (silent coat) I used 50 of them l, you don't need to completely cover the floor you leave gaps.
Then I used 6m2 of sticky closed cell foam 10mm over everywhere and 2m square of egg box foam stuffed behind the rear boot plastics.
Then I used 6m2 of mass loaded vinyl 2mm thick as the final layer. On the boot floor and the cabin floor.
I think I have added about 40kg in weight. And spent 250 quid or so on material.
While it may sound like a lot, the benefits far outweigh the penalty. It's actually made the car less rattly, there isn't any drone and with a hks silent power and a magnaflow mid pipe and an apexi active silencer the car was 74-76db at 79mph.
Pip made me remove the active silencer it's a bit louder inside but you can easily live with it. No worse then any modern performance sports car.