You could probly get one good ten in a 1.0-1.4cu ft ported box that will more than likely sound better than the 3 subs you keep trying to put in there for the cause.It will only cost you some time, and maybe at the most for materials $20 to raise the back seat, and save yourself another sub/sub box, and time.You will get better results, and can utilize the subs you have by building a larger ported/sealed box/boxes for them, and get the potential use from them..IMO.Trust me..Raise that back seat to at the least 12 1/2 in, and youd be surprised what you can do.Seating will not change much for the passengers,if any at all.Save your money,utilize it.