Probably could have used a four post.... but I didn't want to. I use a rod actuated switch, with a small hole thru the rear valence, with a knob.
I use a 3/8 steel shaft welded to the battery tray, die threaded ends for nuts for a steel hold-down.
And nobody has ever checked, or at least I don't KNOW anybody has checked, but I have a carpeted over 1/16 aluminum panel on the package shelf as well as the firewall panel behind the rear seat.