I'm going to have to say that a pair of 10's might be a better choice for a reg cab. If you make a custom box, you should have enough room for ported enclosures and still have a little space to put stuff back there. If you go with 12's, you almost have to use smaller, sealed enclosures. I know that many drivers being made today will work decently in a small box but most of those drivers will produce more db and lower frequencies in a larger, ported enclosure.

It just kind of depends on what sound you're going for, if you want just a hard thump then larger woofers is the way to go. I personally like a nice flat, deep frequency response that sounds good with all types of music. I also think 2-10s can produce more than enough volume level for a reg cab. I'm actually only running a single 10 with about 250W rms going to it. Now I know that my setup wouldn't be enough output for a lot of people but I'm more about quality than quantity when it comes to audio

 

Ok wow just noticed that this thread was started back in September. Who resurrected this puppy?

 

rockford fosgate p1's fit nicly and do very well! also i have a probox that i would sell that fits like a glove