I just typed a whole shitload of good info and lost it thanks to my stupid mouse. Let's do an abbreviated version and you can nut out the whys later.
Consider a solar panel. 80W is good, 120W is better. It will mean you can stay wherever indefinitely without a generator or worrying about flattening your battery. Your fridge will be joined by LED lighting, charging the iPad and phone - and maybe a small radio.
The most important thing to do is use HEAVY cabling. Aluminium cable is fantastic at conducting electricity but it's brittle and not what I'd choose first in a mobile environment, so 8Ga copper (Jaycar sells good stuff) would be my minimum, 4Ga if you can stretch it. ALWAYS put a fuse between a cable run and its power source (take that advice VERY literally). The fuse doesn't protect the battery. It doesn't protect the cable. It protects the car from a fire - if you snag the positive cable against the chassis with a stick and it shorts out, your trip is over unless the fuse protects it.
Charging the aux batter SHOULD be done by something that can fully charge it (ie NOT your alternator). The C-Tek D250S would be my first choice, because it's got a solar input as well and if there's something that C-Tek do well, it's battery chargers. They don't do a lot else, actually!
You could also invert the incoming power from the starter battery and use a mains charger (this is how I do it) but you need to isolate this system with a ignition-on switch, so that the aux system isn't using any power while the car engine is not running (that's how mine works). There's a danger with an inverter - it produces 240VAC which is actually worse than the power points at home - at home, you have an RCD that protects you from a massive shock. An inverter will keep pumping the juice into you until you're a crispy critter. If you choose to use one, make sure its live cabling is kept tidily out of the way.
You CAN charge a battery from the alternator (using an isolator) but this method won't fully charge the aux battery - in fact your starter battery would rarely get above 75% charged. When you work out that you're missing 25% of the battery's capacity to the charging system, you can choose between spending the money needed to increase the capacity of the storage by 25%, or choose a better charging method. Still, if money's tight, an isolator is an acceptable way to deal with it.
What size battery? I worked out that a 160A would power a typical Waeco/ARB fridge for 3 days without too much trouble. That's a big battery (in size) - check its dimensions before you choose that path. You might find it better to get a smaller capacity battery and go solar.
