I guess i will show my age here
but in the "old days" a 3 way refrigerator ran on gas - 12 volt and 110. It had a pilot light so it did not use 12 volt for ignition. It had a 12 volt and a 110 volt heating element. The pilot light would sometimes blow out going down the road with a good side wind so the manufactures added a 12 heating element so you could run the refrigerator while you traveled. If you stopped over night you would have to unplug the tow vehicle or it would run the battery down in it and the camper.
For the way we use our camper a "compressor type refrigerator " would be useless as we often dry camp. But for others it may be just the thing. I watched a video on the you tube where they converted an absorption refrigerator to the compressor type. Kind of interesting.