Lots of people have done it via the 12V battery. As long as you stay below ~1800W you are fine. Just need to keep the car On.
Exactly this! As long as you are aware of how much power you can get away with drawing and keep your power draw within that, I can't see any real issue. A fridge and a freezer might peak a bit high on startup, but the average draw per hour would be well within the capabilities of the Leaf system, the 12V battery should be fine and with however many kWh your main battery still has, this should all work for quite a while (several days probably).
My setup is different, as you would expect as I'm living full-time off-grid and powering a lot more than my fridge/freezer (which uses very little power as it is a 12/24/240V running off 12V. My Sous Vide unit is running today for ~6hrs to cook a 1.7kg chicken, but the battery was going up despite that and is now just sitting on 100%. My stove/oven & hot water are LPG, but each of my 9kg gas cylinders lasts more than 10 weeks so that costs me less than $4 per week. I'm also only paying $50 per week to park my home where I do, so my living costs are pretty reasonable.
Obviously you could set up a system somewhere in between, with a LiFePO4 battery providing enough power to run a few things in the house and solar panels recharging it every day. Basically you can spend from a little up to several tens of thousands, depending on what you want to do. You could set up a house with enough solar, batteries & inverter power to run it completely off-grid and if you could then take power from the car when the solar is not getting enough sun, that would be a super handy backup without needing a petrol or diesel generator.