Now this may vary from coach to coach but on my coach the Fuel Cap (Gasoline) is below and well behind tghe Fridge (Over six feet) Gasoline vapor is heavier than air to the ODDS of the Fridge ignighting the vapors at fill up is negligable.
That said, it's very easy to hit the STORE side of my 12 volt battery disconnect (Which completly shuts off the fridge) as I exit and USE after I pay for it.
As to a fridge starting a fire at a gas station.. I will tell you how it CAN happen.
First: Fridge catches fire: THEN it spreads. (Method 1)
Method 2: RVER with license plate 1D 10 T Sprays raw gasoline all over side of coach including FRIDGE.