Can Someone help me with some box design and cut sheet? wanting to put an 18" in and the way my seats are slanted makes it hard. so i need a box that the rear slants instead of the front.All the dimensions are external. on the bottom i can do 39" Wide and 27" deep. and at the top i can do 39" Wide, 23" High and 15" deep. its for an 18" BL if it will fit and tuned to 35 hz.