Battery in trunk

And this is why it is a good idea to connect front and rear frame rails with a solid connector, I had a 1x2 steel boxed rail welded to front and rear rails which also adds to rigidity.
The floor say is 16 gauge .0625" and the floor is 5' wide that's equal to 3.75" sq that's like 12, 0 gauge cables connecting the back and front. It would take a **** ton of electricity to turn the mid section of your car into a fuse. There's more than enough metal connecting the front and back of your car to start it. Just needs good grounds on both sides.