If you never dry camp, and only need the battery for the times when you're stopped for a couple of hours or setting up camp, a single 12V battery would probably suffice if you don't have a residential fridge. It wouldn't really work well for a large inverter powering a microwave or similar, but for keeping the furnace, fridge, and a few lights going for a bit it's likely to be perfectly sufficient.
Similarly, there's little need to have a three-foot-long, five burner monster barbecue grill if the most you'll be cooking at once is a couple of burgers.