Don't bother. Running an absorption refrigerator on electricity takes a bunch of power, much more than a compressor based refrigerator. 12 volts can't provide enough energy to run an absorption refrigerator at normal cooling capacity, at best all it can do is slow the rate of heat gain a bit. And that's on a single wide refrigerator. A double wide will do even worse.
Why do you want to run the refrigerator on 12 volts? Propane works very well whenever 120 VAC isn't available.