i have done it,
need 2 thick long cables (1 live, 1 earth), Battery terminals, Battery cable ends,
Step 1. Disconnect and pull the battery out of the car (10mm)
Step 2. Pull battery tray (12mm and 10mm)
Step 3. Run 2 whole length of cables leaving 2 feet of extra cable in your boot.
I opted to run the positive connection underneath the car following the fuel and brake lines.
Step 4. Mount the battery box in the trunk.
Step 5. Cut a section of the 2 feet you left in the trunk for a ground cable. Strip, and Crimp one connector on each of the wires. Then Strip and mount the terminals on the other end of the wire to lead to the battery. (Note in order to crimp those BEASTLY 2 Gauge Ring Connectors you should use a Vice!)
Step 6. Ground the negative cable to the bolt in the rear quarter panel. (10mm) The positive should be connected to the positive terminal in the engine bay by taking off the 12mm nut from the terminal and fitting the ring connector in there.
Step 7a. Secure the terminals (Ground cable first)
Step 7b. As soon as you get your battery connected your trunk light SHOULD turn on. If it did, go ahead and start the car to soak up the awesome-ness of having a relocated battery.