No, access was after removing the rear seat bottom. Here watch this video it shows how to remove the bottom of the back seat. Right after that is where I added my ground to where the nut gets removed. I did sand the bottom of the nut to remove the paint so I got a good surface on it.
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If you remove the seat bottom, where the seat backs hinge is where I did mine, using the exact same box you did. Ground worked great but remember to disconnect the Mic under the headliner in the back seat while installing.
No you shouldn't be able to lift it up like that, I had to remove that part while installing my speakers and there are several plastic clips used there which took quite a bit of force to pop. They are easy to break or easy to lose. Take it back to the dealer and complain as that's some shoddy...