Generally you should have 4x GC2 for a residential fridge application. Especially if off grid 18+ hours. Maybe 2x L16 if you have the headroom.
With everything off, your batteries should be resting at ~12.6 volts... plug into the running truck to verify voltage pops up at least 1/2 volt to show the connection is working.
Next I assume you are charging on generator when off grid. What converter is doing the charging? And what is the charging voltage? Voltage should steadily rise to at least 14.2 volts during the first 30 to 90 minutes of charging. You should continue charging at least 60 minutes after battaery is above 14.2 volts.
You did not mention solar? I recommend 500+ watts if you are off grid with a residential fridge.