wiring for vehicle and caravan

Hi I am in the process of undertaking some auto elec work but as I am getting conflicting advice from auto elect, hoping some fellow form members can shed any light before I embark on this common issue. The vehice is a GU Nissan Patrol with standard 7pin plug and the van is a Jayco Eagle Outback with onboard 100amp battery and fridgeswtich.

What I assume:
Car powers fridge whilst on the move but does not charge the van battery.

What I want is:
Car to charge van battery and power 12v fridge when travelling
Install a 2nd battery in van with inverter

What I think I need:
Upgrade vehicle wiring and run heavier cabling (6 or 8mm twin) through a separate socket (ie Anderson Plug).
Upgrade existing 7 pin plug with h/d 12 pin as standard 7 pin connector has a “loss factor” due to terminal size and amperage capacity so I am told.
Upgrade if necessary van wiring to match.
Should fridge wiring be run directly to the car battery via a fuse (is fuse in car or van?)

Do I still need a battery isolator (say Redcarc) fitted to the car as the fridgeswtich automatically disconnects when the car is stationery but what manages the charging to the van battery - is this why I need a separate isolator?

Any assistance will be greatly appreciated. It will help when I go to get quotes as it appears not all auto elect actually understand caravan wiring???