I've had Dometic 3 way (120v/12v/Prop) and 2 way (120v/Prop) and (12v/Prop). I've had the automatic igniters and the manuals. The 12v versions are hard to find now, but you can find them. They aren't efficient, but they can work pretty darn well if you help them out a bit with fans.
With the automatic igniter, I ran with propane with driving, as it was just more efficient than 12v. This worked because the automatic system kept the flame going. With the manual one, I had to use 12v, as the propane would blow out immediately if driving and the system would heat up. If I was using shore power when camped, then I went with 120v, if not then propane.
One thing I did with ALL of them was to add in at least one, and in some cases two (if I had the room) 120mm computer fans blowing up and over the heat exchanger fins. This made a huge difference in the efficiency. Couple things I learned was to mount the fans with rubber to absorb vibration and noise, to make a little aluminum deflector to more direct the airflow. If using two fans, I'd have one blowing up and onto the exchanger and the second pulling the air out of the exchanger area and exhausting out the side vent. I've also tried putting little fans inside the box, but I could never really tell if it worked better or not.
Also, an old trick with absorption fridges, if the unit quits working, as in flame/heat is on but not getting cold, pull out the unit, turn it upside down for at least 24 hours. In many cases this gets it working again. Modern units are not as cantankerous in demanding exact level conditions, but the more level the better.