2011 Silverado crew cab box and sub help.

I have a 2011 Silverado crew cab and I am looking for the best sub and box option. I have a Rockford fosgate T1000 amp for sub or subs. I was looking at the ground shaker under seat box and was going to put two Rockford Fosgate Slim P3s in it. My issue is air space. Yah the subs fit but is there enough air space to really pound? I also considered getting a T1 Rockford Fosgate slim and blocking one opening with wood or a 12 bass radiator passive speaker to get enough air space. Any ideas?