Have you measured the draw of your fridge? You can do that with an ordinary multimeter -- there are instructions online about how to do that. If I can do it (and I have), anyone can.
Once you determine the draw, you can calculate your battery capacity and see how long you can handle the load. Remember that a 110 amp/hour battery (for example) can only take about 65 amp hours before it gets down to 50 percent state of charge -- I think that is when the voltage reads 12.1. Any lower, and you risk damaging the battery, or so I am told.
2012 Fun Finder X-139 "Boondock Style" (axle-flipped and extra insulation)
2013 Toyota Tacoma Off-Road (semi-beefy tires and components)
Our trips -- pix and textAbout our trailer"A journey of a thousand miles begins with a single list."