Installation of Power Outlet in Truck Bed

Hi all,
First time post here. Just bought a 2000 Tacoma PreRunner (3.4L, AT) last weekend. I love it! Looking forward to lots of adventures with it in the near future. I bought this as my 87 4Runner (360k miles!) is finally starting to really crap out, and I just didn't want to keep putting money into it and wondering what the next problem is going to be. I will be sad to see it go...had it as my only vehicle since 1990!

One of the first things I did with my new Tacoma was to mount a new truck tool box in the bed. Worked out great! What I want to do now is install a standard 12V auto power outlet inside the tool box, so that I can keep my LED flashlight charging in there while I'm driving around. I may plug other devices into it as well (say like my thermoelectric cooler). The problem I'm struggling with now is finding the most convenient and accessible place to connect it to 12 volt power. I'd like the 12V outlet power to go off when I take the key out of the ignition, so that I don't risk draining the battery. I already bought the outlet (dual), 12 gauge wire and a 20 amp inline fuse. I'd like it to have its own 20 amp circuit, rather than have it shared with the other power outlets in the cab or other electrical devices. I'm sure if I studied the schematic and inspected/tested the truck I could probably figure it out myself, but I figure I would check here first? Has anyone done this kind of thing before? Thanks for all help...it is much appreciated!!