I was sort of thinking along the same lines. I did a bit of Google searching and found this link. Not sure if any of these are any use, or any better than what we have, but at least they offer something to look into.
http://www.gas-refrigerators.com/
Serval brand fridges, which are Swedish in origin, used to be quite common in our area where some people have private natural gas wells. This was back in the fifties. It seems that Serval morphed into Dometic for the N. American market. Serval was taken over by Electrolux (also Swedish and now the parent company of Frigidaire). Eventually Dometic was sold off to a European venture capital company, who in turn sold it to another venture capital company. I take this to mean that Dometic is now owned by people with no technical background in the field, and whose primary interest is in making money by buying and selling companies, not producing inovative products, The early Serval brand gas fridges date back to the thirties or before, and apparently some are still running.