Donald, I am putting in dual 10's (using shallow Pioneers [got a great deal online!]) under the rear seat using a box I bought from Supercrewsound. At the moment, I have the factory amp feeding them but I did a dry run with a new 400 watt RMS amp today. Dry run meaning I laid the amp on the floor and ran the power cable out the door, alongside the truck and tied it to the battery. I just wanted to see how it sounded before I went to the trouble of mounting it and doing a full install. There is so much bass coming out of that setup that it's TOO much for me! In fact, I couldn't dial it down enough for everyday listening! I'm going to need to attenuate the input to the amp with an outboard control. In summary, LOTS of boom! Your mileage may vary. It actually sounds pretty decent with the factory amp to tell the truth. But of course, having separate amp will ultimately give me better control once I find the right input level.
Sorry, I don't have a full size 10 or 12 to compare to. That would be interesting.