RE: Fridg on 12v
Actually, the refrigerator will run the battery down in 2-3 hours.  Why have
the 12v at all?  Some people ( and many RV advisory sites) warn against
running on propane while driving.  The lit flame poses a small but real
hazard in the event of an accident and spilled gasoline.  You also don't
need to turn off the propane when filling the propane tank, it's already
off.  (And if you don't put your propane frig out when filling the the
propane tank, think about that overflow valve venting raw propane about
eight inches from the flame).  Running on 12v  on the highway also means you
can make short stops and the refrigerator continues to work (if wired
properly to the aux battery).  This does not apply if the aux battery is not
installed, it will be shut off when the ignition is off if still wired as it
came from the factory, on the starter battery.
BTW, I usually run on the road with the propane on.  To many times I forgot
to switch over while making camp or was delayed and ran the aux battery
down.