single 10" in reg cab = not bad
This is the first time I've had a reg cab truck, so when I put in a $100 ten-inch sub I was quite impressed with the bass. It was def. loud enough for a reg cab since there's no back seat blocking the air movements of bass.
The only prob. is that I was using an elemental designs (small-box) e10k in a ~1ft^2 sealed cube-shaped box. The appropriately sized box gave the sub enough space to really move on those low notes. Getting a truck box might mean losing volume; thus sacrificing sound quality (and yes, for me...that's important).
Also leaving the (obvious-looking) subwoofer box above the transmission tunnel around where a center console would go, would be nothing short of a "steal me!" beacon.
Let me see if I can take a quick pic so you guys can see...