Got an isolator in the post today, it was not my plan to have an electronic isolator, but this looks the simpler option for the wiring.
I ordered it with a blue button so it would be easily distinguished from the fire button, the kit comes with an interior on/off button and a external kill switch. I am going to mount this where the rear seats used to be, I also went with the high capacity version, just incase I swap the engine to an M3 unit and need the higher load capacity.