Its in the boot under the floor out of the way
My first set up was a National Luna duel Battery controller, it was a good unit when I first bought it about 8years ago .
I have a diesel so the second battery was a Blue Apple battery pack, what was connected with a 125amp Anderson plug. I use to keep it in the passenger foot well, when we went camping and remove it when not in use.
It worked ok but not ideal, about 2 months I cut the rear boot out and installed a larger storage tube. I should of done this in the beginning but I didn't want to cut into a brand new car, now the car is old who cares now.