Here is what we did to our hatch.
1) removed the trim panel obviously
2) check all the wires and parts inside to ensure none could rattle, used some silicone, tie wraps, etc, to fix the ones that could.
3) stuffed a few junks of accoustical foam into a few areas to give them some support, keep them from resonating.
4) used some very thin aluminum sheeting and covered the access holes into the hatch with it, self taping sheet metal screws were used.
5) removed the rubber isolated resonate reducer(apparently what it is intended for) this saved back part of the weight the mat and aluminum added.
6) Matted over just the plates we installed and onto the stock metal to seal up the holes.
7) Sealed up any remaining holes that are not used to hold the pops for the trim panel, used small patches of mat.
8) Covered(not yet done) the whole area with a layer of ensolite foam, cut our around where the panel pops go so no fitment issues.
We did not mat any of the outside skin, not needed in this situation.
When we finish up the rest of the car and replace the trim panel we are going to cover the back of it with structural expanding eurathane foam then use a dab of silicone sealer on the mounting location for the pops then some on the pops where they plug into the hatch. This is a very important step, not to hard to take apart again if needed in the future.
If all that is not quite enough we will use a very small bead of clean silicone around the hatch trim panel where it meets the hatch.
Excessive? depends on your point of view
Amount of mat and foam needed? Hardly any.
Added weight? barely noticable.
Pay the shipping, just a few bucks, and I will give you some left over pieces from our install to play with
Email me your zip code, [email protected]
Obviously I cannot do this for everybody though, lol!