If you would rather go for a more permanent installation and not have to worry about forgetting to unplug the 12v adapter, you can wire in something like this.
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You should be able to determine what fuse you can use at the panel under the rear seat, if you have a DMM find a good place to hold ground and check fuses that you may not use like Rain, Sunroof, etc. Check each side to see if you have 12v, or 0v. Then after selecting a fuse make sure it gets 12v with the ignition on. If you do not have a DMM go buy one they are about $15-$20 at Walmart, they will save you alot of headaches in the long run and are a good solid investment.
Now that you have selected your fuse, run the black wires to a similar location, I used a ground I found in the panel on the B-pillar (overhead monitors). You should be able to use the seat bolts, or something similar I would recommend against using the 12v sockets ground as it can cause interference. Now under the seats you may notice that you have flaps in different areas of carpet, you should be able to find one under each seat, and under the rear near the fuse panel. Use either a wire coat hangar (be gentle), or you can get the proper tool at most auto stores which is a rubber coated wire to help prevent snags and damage to wiring. Hook up to the fuse and it should come on everytime you start the truck.
Take the time to it right and you will be much happier in the long run.