need help/ advice cutting trunk/cabin access corners
 

Ok so I have a 2 dr 02 cavalier. I have a sound system in the car and my problem is my subwoofer box is to big. In order for me to slide it in through the rear seats being folded down, I would need to cut the corners that are covered by the plastic covering. I need to cut the each corner of the metal out to slide it in. My question is, is this a major structural support of the car, or will I be able to get away with cutting the corners out