I am about to mount a second battery in my '06. Just inside the rear compartment is that space to the right. At least 75% of the battery will fit inside there. I'm putting it in a plastic battery box with a ICT billet mount inside the box. Running #2 copper from the front battery, with a 100A fuse, to protect the primary system from a possible short-circuit between the batteries. Purposes of my rear battery are the rear winch (mounted on a plate welded to a hitch bar) and a 3KW AC inverter, just 'cause I may want some 110 one day. Both of these will have very short wire runs to the battery, so that they will always get full voltage.