I suggest you start with the trunk,
it is customary to apply dynamat " thick asphalt based rubberized sheets to the trunk floor but I and many others who tried both have found that isolating the trunk floor with a wooden board or better some acoustic board like the ones they use on walls shaped like the trunk floor would help much ..
actually I foulnd out the earlier contours used to have a wooden board on top of the spare tire in the past ..
try to custom cut a board and fit it on top of the spare making sure it covers the whole trunk .
next you should sound proof the area under the rear seat and around the tire wells with sound proofing materials.
do a search on the forums and you will be knocked off with the amount of info you can get.
