Extended cabs are pretty easy..

I used about half a sheet of MDF($25.00) and cut out that little tool holder on the drivers side and stuffed 2 8inch subs under there... It's working good so far and I didn't spend $150.00 on a box..

I have some pics of the finished product installed.. send me a pm for pics... (also believe I made a post after I finished.)

 

I'd go with the 10's
you won't be happy with just an 8" i've got a reg cab and ran an 8 for awhile,
not nearly enough power for me

 

anyone know if 2 12's would fit under the back of an extended cab. i have them in a bandpass box in my jeep but when my sister goes to school next year there going in the truck and i was wondering if i could cusutomize it to make them fit under the back seat.

 

I currently have a 12" in a single box sitting on the rear seat. I can still fit 1 person back there (2 squished, but have fit 3 girls back there with the sub still in ) It sounds really good, and hits a lot lower than the 2 10's that I had. Also if I need to fit people in there, i cant take it out in about 30 seconds and re-install in the same amount if time. It works for me...

 

I used to have two 12" rockfords sitting on my back seat. I just put two 10" kicker VT's under my back seat with a phenix gold 900 watt amp. and they sound soo much better then my old rockfords. now I just gotta get a new CD player. and I have rockford speakers in the doors and back.