I personally would not go as far as taking out the rear seats (and asking Tesla Service to do it will likely involve them putting in a permanent note on your car's history that this operation was done and will haunt you re: warranty / resale).
If you have bothersome rattling from the car's amplifier which should be located behind the tail end of the passenger-side panel, you can put some sound deadening material in there; otherwise if you want to treat for road noise and the booming, do it from behind the wheel liner (outside the car) where you'll have better access and likely better results. Having the closed-cell foam on the outside lining should prevent a large percentage of the noise and vibrations especially from the tires from being transmitted and distributed through the car's body (where it becomes boom).
Following performing the front wheel wells (
#41 &
MountainPass Performance Comfort Coilovers) which improved sound levels immensely, I did this recently for my rear wheel wells (also treated from the inside panels, though not as comprehensively) and there's a big improvement in noise reduction, especially in tire and road noise; and further reduction of booming. Performing this for the front wheel wells produces a bigger improvement especially for the front passengers; I only took pictures while performing the rear (you can see I also have the MountainPass Comfort Coilovers and MPP rear camber arms):
View attachment 674233
View attachment 674239
The outer parts treated with butyl are especially thin and resonate if tapped. Rest of the surfaces are rigid enough to not need butyl.
View attachment 674238
View attachment 674237
closed-cell PE foam, being careful to keep overlap to a minimum so it does not lead to issues refitting the original wheel liner:
View attachment 674236
View attachment 674235
all back together:
View attachment 674234
.. and yes the car is finally quiet.