Found RCA cables.. No power or ground?

Hey guys, I'm new here.
I just picked up a 2005 Double Cab TRD Tacoma with the 6 speed trans from the dealership that I work at. I was digging through it and cleaning it up and I came across some RCA cables behind the driver side rear seat. Funny thing is, I found no power or ground cables running back like for an amp and sub setup. I don't have the JBL sound system, but I do have (what look to be) factory Rockford Fosgate speakers and tweeters in all four doors.
My question is, could there be a factory harness like the JBL systems have and he just was running a factory JBL system behind the seat? Or why would there be RCA's but no power or ground unless I am just missing them? I suppose he could have removed the power and ground, but I am not sure because he left the RCA's.
I would like to install something back there, but what would fit in there with the factory plastic bins and such behind there?
Let me know what you think.
Thanks!

 

IMO the wires were expensive and worth removing.
My amp is under drivers seat-1/2 of it.

 

That's what I'm thinking. Some kits get pretty pricey just for the power and ground. RCA's are pretty cheap on average. Maybe you're right.
What sub could he have had behind the seat though? I could easily run the power and ground. I just can't figure out what he could have had back there to fit with all of the plastics and such behind there.