What is your total budget? What are your goals? So you want under the seat, and you want it to sound great with many genres of music. Do you have amplified speakers or no? Answer these questions and I can point you in the right direction. I wouldn't use ANY of the equipment mentioned in this thread so far. The mainstream stuff is poor quality with marked up pricing. Old-school motor technology, lack of copper, low quality parts...at least get a solid-built driver.
Total budget isnt really a main issue. As the system isnt needed right away. If i have to save up a bit longer thru the winter (truck its for is summer only) it'll be good. But im not looking to get too crazy. maybe 1-1.5k? AT the very most, but not looking to spend this if at all avoidable. I dont need it to hit so hard it'll jar your brains out of your head, but if the time was needed, i wouldnt mind being able to crank it up a bit. Just to add some extra bass to it. I'm running Pioneer door speakers, not amp'd. And im only running under the seat as i was given the box, and it still leaves my back seat, which i do need the room. but if i can get away with a single 10, or 12. i'll buy a box that will work with it I'm just looking for ideas to get this squared away.
I have to kicker cvr 10s under my back seat. There in a box made for a 4 door chevy. The bottom of the seats sit on the box and have 0 issues that way. I'm running a 800 watt audiotec amp. I also listen to different genres of music and I'm happy with the sound. It hits hard enough to be heard coming down the road.