its pretty easy to do for legality reasons you'll need to put a sealed battery in the boot as well as a battery box because the cops are know going to the extent of saying that the use conventional battery expell gases which requires ventilation, something that the boot doesnt offer, this is the only thing can defect you for, it more of a safety issue there trying to tackle as well as taking your money for revenue,
but as for whats required you;ll need enough wire to run from you current battery location to the boot, i use zero guage but 2 or 4 gauge is fine, just increase the cca rating of you battery to reduce voltage drop.
you can do it a few ways i use a distribution block like those used in stereo installs can be bought from super cheap. this will allow you to remove the battery fitting from the positive and put all the wires into it and then run the new battery cable to the boot, the negative terminal can be bolted to the chassis, and do the same from the battery negative to the chassis in the boot,
i find this the simplist way the do it, hopefully this makes sense