Can't reverse mount as I won't be able to get the box in the trunk.They'll be fine. Use aeroports and reverse mount them to eliminate driver displacement if you can.
If not, you'll still be fine.
So let me make sure I got this correct. rl-P 12's need a min of 20 in^2 per sub of port area. So 40 total.One 6" aero about 21" long should do the trick. That will actually be 3 cubes net tuned to 32hz.
21"'s .................................. wow, like the size of my step moms dickOne 6" aero about 21" long should do the trick. That will actually be 3 cubes net tuned to 32hz.