My 17 has the 5 cu ft fridge, which does not have a 12V mode. The 5 cu ft is pretty much a manual refrigerator - no electronics board, etc. When mechanically switched to propane, it uses a push button to fire a piezoelectric sparker. There is a neon indicator lamp that flashes in time with the spark. Once the gas is ignited, the sparker shuts off. There is a flame sensor that immediately restarts the sparker if the flame blows out (I've blown out the flame while the trailer was stopped to see this happen).
I had many problems with running on propane while driving in the past. I have a remote thermometer readout in the RAV4 & could watch the refrigerator interior temperature climb any time I drove over 40MPH. I don't think the flame was blowing out since it immediately began to cool down when ever I stopped (without pushing the reignition button on the fridge). While I have no way of telling for sure (since I can't ride in the trailer while pulling it over 40MPH to watch the spark indicator) I have to assume that the flame is still on, but not providing heat to the system. If the flame actually blew out, I find it hard to believe that the gas valve was still open & spark igniter trying to light it while driving down the road.
Finally got tired of the problem & did a number of additions & modifications that fixed it. I'm not sure which solved the problem (or which combination) but I added a furnace filter to the lower grill, added 2 baffles, one at the bottom to direct incoming air away from the fiberglass shell & onto the cooling fins, and a second at the top that is curved & directs the air flow to the top grill. The instructions for the baffles are at this Dometic Vent Installation PDF
I also insulated the area around the outsides & top of the refrigerator & sealed the edges with aluminum tape. The last modification was to add a 12V box fan to the upper grill. It only helps when the outside temperature is over 90°F.
All this probably doesn't help with the new refrigerators, but might be helpful to those having problems with the older 5 cu ft model.