buy a plastic battery box from ripco/supercheap
find CaM's thread and copy what he did, cos thats what your gonna do anyway
you'll need:
battery box = 40 odd from ripco
new cable = expensive, bout $10/m from like jaycar when i looked into it for thmini
crimps = box from ripco/jaycar bout $15
isolating switch = $20 odd bucks, repco/jaycar supercheap
cable clamps to secure cable to car =box from repco/jaycar $15
mash a couple of steel plates sandwiching box to bottom of the boot floor (steel panel, not the wooden false floor) use the original clamps secure to those steel plates, or possibly get new clamps to suit