Controversial opinion: If you want a "dead" car, buy an Audi.

Foam also likes to hold moisture & used to be a seed for the Tin -worm (rust)

When empty it must resonate a lot. Some old 80s luxury car a flatmate had the tank had a 3-4cm thick foam between rubber pad on top of the tank to reduce noise. So guess there is something to it. But awd cars the tank is pretty solid since it has to clear the driveshaft.  

A friend put sound deadening on the fuel tank and said it helped a lot.. could be another place to think about.

Well I’ve not driven the car yet but just in the car park the reflected sounds have dropped noticeably while installing it. tapping of the treated vs untreated was obvious, not dead like the tar/rubber mat but no ring. Very surprised now much different given it’s so thin and light.   If the heat is reduced as well then will be wishing I did it years ago 😒