Battery relocated to trunk, inertia switch?

You have a link, part no. etc? Or even post a photo? Any inertia switches (that is OEM) are "latched closed" and open a circuit. So that would require a relay (or transistor etc) to invert, etc not sure how you'd implement that. Same problem, "draw on shutoff" Adding more circuit adds to possible failure, and defeat the purpose.
Painless Performance 30206 Painless Performance Remote Master Disconnect Kits | Summit Racing mine shuts eveything down but the radio memory and the ECU