For the purposes of this thread, ignore the black box, its a PC-Relay interface. Hence the parallel cable on the left hand side.
Yes you could make a bus bar, or Durite et al stock different versions, stud, screw,4,6,8,10,12 etc. you can get bus bars intended for +ve use, they come with a shield that fixes over the connections. The negative bus bar i have is insulated from the bulkhead, its base plate is plastic.
It's where it is because the battery box has two batteries in it, and the bulkhead is higher and thus (most of the time) drier.