Hey everyone I just had a simple question, i have my box in my trunk of a 2000 chev cavalier and was wondering what is better for max SPL, having it face the inside of the car with the seat down or facing inside the trunk towards the back of the car?

Try them both and compare. In my 97 cavy, laying on the folded down back seat, facing mainly up with a slight tilt forward turns the whole inside of my car into a wind tunnel, it's great.