I decided to add a 2nd battery to my 1996 Aquasport Explorer, did some research and found this kit:
Here is how it use to look:
1st Step move the wire harness back to the corner, there is room in the loom to push the wires back:
2nd Get two battery trays and then mount the batteries in them like this:
Here is another view:
... I will write up the next steps as I do them next week.