Thought about doing that exact thing because I have the rear seats deleted. Does it make a good difference? Want to get new clips for the rattling and deadening to quiet the wheel wells down . Also probably throw some in the hatch too
As you probably know, the kilmat doesn't do it alone. The mat is meant to quiet metal that can resonate and/or amplify noises. And I used the thinner one to minimize weight and costs! Originally I did the spare tire well and just the deck from tail to rear seat well. No ensolite yet. I did NOT notice any difference.
I knew most of the noise when the rear seat was down was coming from the rear tire wells. Now that I have the wells fully covered, but not above them, I should give it a test, but honestly, I'm rushed for time and already planned to add the ensolite. Well, that and there are so many little sections under that little window with so many attachment points for wire straps and such. Then you have the holes for the retainers. Ugh, it's a pain for sure. If I had the time, maybe. I can always go back AFTER I do the roof liner and moon roof.
Under the little windows, I tapped on the metal to find the highest pitched places and put a little kilmat there. The ensolite should handle the rest. I say this bc as of Friday night, I'm not finished... I will be "finished" Saturday and will take a test ride. If it needs more kilmat, I'll add it next year.
I also put ensolite on the back side of the side cargo carpet well covers and plastics. I figured it was easier then working around all the stuff mentioned above. Still a pain. It creates a wall surrounding the cabin, rather than directly on all the metal/kilmat. Yes, I left the vents open on the side carpets. Those that have never looked behind the carpets and plastics.... you're in for a surprise at how busy and convicted it is.
Anyway....too much rambling.. I'll let you know tomorrow and edit this post below.
EDIT/UPDATE... With only a very short low speed drive to test it out (40/45), I could detect some difference; however, I'm not sure how much difference. I really need to get out on the highway Sunday to know for sure. In fairness, I have not covered the kilmat on the deck yet either. I do have some foil/Kraft paper backed ensolite for that. I just ran out of time. In the meantime, I did put a yoga mat over the whole spare tire and deck well area for sound insulation and roadside troubleshooting.
When I was putting the plastic pieces back over the triangular window area, I thought if needed, I could put some non-adhesive ensolite over all the sensor wire areas and use tyvek tape to secure it. That way I get the sound insulation and it's still removable in the future w/o gummy adhesives.
2nd UPDATE... after testing up to 80mph, the annoying high frequency swishing/hissing road noise/aero is gone. The mids are mostly gone and of course, lower freq such as the exhaust, are still there, but I would say less pronounced. Of course, ymmv since all of this is affected by the thickness of sound deadening and ensolite rubber used. On the back side of the plastics, I used 3mm enso. On the the metal I used 50mil kilmat. I have 5mil enso for the deck surrounding the spare tire, but will also cut the yoga mat to cover it all.