Well I am thinking of putting in a separate 12v system.
It can be isolated from the main system except when charging.
Of course it can slow down main charging if it is quite low.
I am also considering a fully isolated system at all times. Wire in marine style on board charger and tie it into the incoming AC leads. So still gets charged when the car gets charged, but puts no extra load on the vehicle systems.
Most of my driving will end up being highway for 60km at a time. So 45 mins or so. The aux 12v system should stand up just fine with the short on time and being recharged after each trip.
But even at 80A, that's tons and tons to charge the aux battery as well. But to maintain range, it would be isolated during driving.