Save yourself the time and do not do subs up....it is the worst...i went that route first and then found out both forward or backward sounded way better,
Design like a v-shaped box facing forward or backward....
Apparently you didnt do it in the right car then. Cause it works extremely well in open backed cars, such as SUVs. I did it in my SUV and it hits pretty hard. Its the the best set up for a trunk
P.S. my sig is my old box