That new box looks very much like the NMW battery box.
https://www.yenko.net/ubbthreads/ubbt...9&page=all
I had fun reading through this old thread and it brought back a few memories how we installed trunk mounted battery's back in the early 80's.
Just like another form member we used the metal tray mounted through a plastic marine box. We then got a used industrial welding cable that was in good condition.The welding cable was a great conductor and had 0 voltage drop.The down side was it was over sized and heavy, I would not be surprised if the cable did not weigh 25 + lbs. We chose the used welding cable because it was given to us for free. Back then we made a lot of our own performance modifications because we did not have the money to buy them in kit form so we improvised.
Today I would go with a NMW style box and some light weight cable. If you go to the trade shows check out the new performance battery cables they weigh next to nothing.