what i would suggest is a capacitor, second battery (medium gel cell works great), and an orion mbr70 (don't know if they still make it), but it's better than an isolator in which it is a smart circuit (multiple battery regulator) that isolates and then couples the batteries together when needed and isolates them when the engine isn't running. i used one when i was into stereo shows and it was awesome.

i've got one if you are interested since i'm no longer running a high wattage system.