I'm working on a solar power system for camper conversion in a 2019 awd xle. Want to be able to charge the house battery by both solar and alternator. Have it pretty well figured out except for how to run wire from the starter battery to the rear space where the 3rd row seats were stowed, which is where I want to locate the house battery. Specifically, how to get wires from the engine space through the firewall and into the interior. Any info or ideas for how to do that?