I think the series of events occur in this sequence.
The switch is turned on which activates the fan motor
The fan blows against the sail switch which then activates the ignitor, this is where the 12 volt voltage comes to play, if the fan does not turn fast enough the sail switch will fail to activate the ignitor.
Then the gas valve activates to complete the cycle.
If the sail switch goes bad, or the circuit board, no ignition will occur.
You can call an independent or mobile rv repair person and they will sometime assist you through a proper diagnostic procedure. Also some rv repair places have a circuit board tester that can rule out whether you have a circuit board on the blink. Replacing parts without a proper diagnosis can get expensive.
Also, you are correct, I've heard of a number of cases where the cold had effected the propane flow. A few have heated the propane tanks with a blow dryer or other means, to find it resolved some issues.