I'm pretty new to this, but I'm pretty solid in wanting to learn how to build my own boxes, I want something for my budget and currently that is far less than the space I'm willing to use. I'm looking at running 2 Soundqubed SDC2.5 15's or 2 HDS215 subs in the back seat of my extended cab silverado using an RE Audio CTX 1600.2. The space I want to work with is 54in wide, 26.5in high, 24in deep ~19 cubic feet, I want both the subs and the port facing the seats, the square port would be 25in high and 8in wide and about 11in deep. I was wondering would utilizing that space for only 2 15's be worthwhile since I'm not using the space for anything else, or will it actually hurt my subs performance in such a big box? If so, how far should I downsize from this box, roughly?