So long as it's (reasonably) level, there's no harm in leaving it on. There's also no harm to the fridge in turning it off. Ammonia gas doesn't have particles to settle out, and doesn't go bad with sitting; neither does water or hydrogen gas.
Running on electricity, an RV absorption fridge uses somewhere around 3-5 kWh per day, roughly speaking. It does depend on the outside temperature and the fridge model and so forth, of course. A standard residential fridge is a few times more energy efficient on AC power than the RV fridge, so it doesn't take very many years for a cheap one to pay for itself if you use the RV fridge as a spare/beer fridge at home.