This is the set-up in my race car with 2 batteries which has been great for years as I never have an issue with enough power for an entire day at the track.
One of my street cars has a single battery in the trunk as well.
It is important to run both positive and negative to the front of the car to 2 distribution junction blocks, one positive , one negative.
Do NOT use the frame or body for any power or ground path as we found years ago it will cause issues.
View attachment 262286
Pics of the junction blocks up front please???