Keep in mind this is a Chevy silverado crewcab.
Underneath the backseat are 2 8" kicker L7s, behind the seat I plan to put 2 10" kickerCVRs behind the seat.

Will this sound bad? If so what sort of subs would you recommend putting behind the seat?

It's my 2nd system and I don't know very much about multiple subs but I'm keeping the dual 8" subs due to money and I don't want to have to buy another custom box and speakers. If you were in my position what would you do (what size/how many subs) ???

Thanks in advance