Propane or battery

I need to keep my freezer cold during 10-12 hour days of driving.  Is it safe to run it with propane while driving?  Or should it be on battery?  If so, should frig be switched to propane while stopped for what length of time?   This will be my first real long trip;  usually I get the frig cold, then turn it off while driving and typically don't use the freezer.  Thanks for your help

Run the fridge on propane. Many tow vehicles are limited in the amperage they can supply to the trailer due to small wiring. The fridge on 12V draws 10 Amps by itself which leaves very little to charge the trailer battery. Running the fridge on propane ensures you will arrive with cold ice cream and a fully charged battery. As for the safety argument, consider that most fridges larger than 5 cu. ft. don't even have the 12V option. They travel quite safely on propane, and you don't have to worry about forgetting to switch from battery to propane when you stop.

+1 to everything said.  I'll add that I wouldn't worry about turning it off at gas stations.  Gasoline vapors are mostly recovered either by on-board vapor recovery systems (all modern cars and trucks have this) or by a system on the fuel pump.  Whatever may escape is heavier than air so it will sink to the ground, while the flame in the fridge is 2 feet higher.  Additionally the slightest breeze will whisk the fumes away anyway, and even if they do find a flame gasoline has a fairly narrow flammability range.  A little too much air or too little and you could take a blowtorch to it w/o a problem.

   We always traveled with the refrigerator on 12 volts except when at a rest stop then was switched over to propane. We had the tow package on our tow vehicle with a heavy duty electrical system included. With propane I think that it would keep a colder temp which is helpful if you have ice cream.

With the low flow safety valves on today's propane cylinders it would be closer to those trigger operated butane fireplace lighters.