I'm going to try to tackle over the winter.
I have NO experience with cars but worked building offices for years in buildings where we tried to keep noise from being transmitted to adjacent offices from audio/video/boardrooms, etc. Hence, I subscribe to the school that you use a layer of dampening material, a layer of close coupled foam, a layer of sound blocker and if you have the additional space, some sound absorber.
This is the site I found valuable.
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My intentions are to do my install following this guy's methods. It remains to be seen what room I will have on the sides of the hatch and the doors. I see no issues with the hatch floor.
It looks as though I need at least 3/8".....more would be a luxury. The layer of absorber may wind up being deleted on the hatch sides and doors.
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