FYI, aftermarket stereo installers run 12V to the trunk all the time to power amplifiers, equalizers, etc. No big deal.

You figure out what you will be powering to know the amp draw, you decide then to use 1/0 gauge, 4/0, or 8/0 wire, then buy the components (connector, fuse holder, wire, etc), and then take an afternoon to pull the wire from the battery through a rubber grommet in the firewall, through the dash, under the carpet in the plastic wiring channel, and through a grommet into the trunk (you may have to drill a hole). Decide where you want the 12v outlet, mount it, and wire it.

http://www.crutchfield.com/g_714/Power-Cable-Terminals-Clips.html?tp=2357

Install the fuse in the holder under the hood.

Done.

Tres facile