hey everyone i have a 98 chevy ext cab and have taken out my back seat. i have RE audio sx 18s. i need input. i have a box built that was used in a truck like mine but i want it bigger. or would using 1 18 with a bigger box make a bigger deeper sound? im thinking about 8 cu ft tuned 30-32hz. or taking up the whole back of the cab. but i would need some assistance.