First, don't bother with the full disassembly of the rear of the car just yet. Get 2-3 old shirts and crawl into the trunk. There will be like 4 rectangular ports that lead into the rear deck (they're obvious when you get in there). Start jamming the shirts into the holes, pushing them up and in different directions. I got 2 t-shirts and like 3 socks up in there.
Result? Completely silent. Yeah actually removing the deck (which involes the seatback, the c-pillar covers, and breaking a few clips along the way) and placing foam is the proper way, this one works just as well functionally, and the ghettoness is hidden from view.