I have chassis grounds at the front umbilical connector and in the rear closet by the converter. The rear rear wire runs to the ground lug on the converter and the battery cable on the fuse panel.
How much of the 12 volt
system is original? in mine the PO put in a new converter with the old fuse panel mounted on a board above it. Originally there was a 50(?) amp ground side fuse mounted on the floor on the main cable. It's since been mounted on the board. Many fuses and holders were loose, had high resistance or were blown when I got it. They all have been cleaned, tightened and had new fuses installed.
There was also a quick disconnect on the battery cables that had melted one side and was loose on the other. I replaced both cables to the converter.
Just thinking off the top of my head,