i looked to do the exact same thing for my trip to france - only problem was the cool box took up most of the boot space so i decided against it.
it should be pretty easy to hook up as the battery is in the boot, i planned to just clip it into the battery & either cut a hole in the carpet or run the wires up to the side - just make sure you fuse it & switch it off if your away from the car for a while as it could run the battery down.