I did actually remove the plastic nut for more clearance behind the subwoofer.
The steel frame is fixed to the car chassis using the original bold of the spare tire. Then the top cover is pressed to the steel wheel by 4 bolts connecting the steel frame below. There are rubber foam sheets in between these components to seal the subwoofer.
I also have to add a wrench to remove the wheel as needed. Therefore, all of my bolt nuts are the same size for this reason.
The steel frame is fixed to the car chassis using the original bold of the spare tire. Then the top cover is pressed to the steel wheel by 4 bolts connecting the steel frame below. There are rubber foam sheets in between these components to seal the subwoofer.
I also have to add a wrench to remove the wheel as needed. Therefore, all of my bolt nuts are the same size for this reason.