I have my 2 12's facing forward and they hit pretty hard. I think down facing are good as long as they have room to breathe. I dont think its good for the sub if its right on the ground, but I could be wrong.
I have always heard that the bass "sound wave" needs some room to bounce off walls to help with sound. Since our trucks are small anyway you install them they should hit hard.
2002 - XLT, 4.0L, 4x4
3" BL, 295 Nitto Terra Grapplers
K&N FIPK, Dual exhaust