Ok, now a bit of background. In the real world I am an electrician, not an auto electrician, just an electrician so go easy on me if I accidentally use a bit of lingo.
Most of us will need (or should have depending on the budget) a “dual battery system”. Put simply this is an additional battery in your 4WD, besides the main battery that starts your car, that is used specifically to run your fridges, camp lights, and any other little luxuries required to keep everyone happy. This should be installed in a way so that it is isolated from your starting battery. This way if your fridge is working overtime cooling down some cans of amber ale, your car will still start when you want to leave camp, even if your battery is totally flat. This is where solar panels come into play.
When you are driving, your car charges the batteries connected. When your car is stopped, no more charge. Solar panels can plug into the “charging system” which will then charge both the main 4WD starting battery and the auxiliary battery.