the carpeted piece under the rear window. I'm referring to the piece that the speaker sticks out of? Also, what are the 3 things sticking out of that same piece that are covered with a plastic clip called? I'm missing 2 of the covers and need to know what to ask for. Thanks.

 

Those plastic covers in the back cover the child safety anchors for car seats. The rear deck isn't that hard to take out.

1) remove back seat
2) Pop out plastic sides inside car
3) Undo clips on rear deck and lift and pop up clips holding it down.

You'll need to unhook the seat belts if you want to take the rear deck out.

This thread may help aswell.
https://maxima.org/forums/audio-electronics/35462-playstation-2-question.html

 

this is helpful info since I'm thinking about cutting a hole in my rear deck to keep from letting my seats down so my sub is louder. I saw someone do the same thing and cover the hole with a Bose grill so it appeared stock.