It's not the propane that's the issue. It is the spark igniter. So if pulling in for gas go in and turn the fridge off this will turn the spark ignition off and you can fill up.
Now the second part is fuel vapor is heavy so it will be at ground level so if you think about it you should be fine and also you are at a gas bar which is a fully open area with lots of wind moving air so gas vapour should be dispersed with no real issue.
If you are really worried about a spark fire then when you pull into a gas station you should roll in without your vehical running and push your vehical back out to a safe spot after. Think hard about all things in your vehical that have spark things like spark plug coils,starter motor that's mounted under a vehicle,heater blower motor,power window motor,static electricity. As you see lots of things that also spark that could cause a spark ignited fire. But yet we are not all blowing up.
I did a big road trip last year and yes filled up with the fridge running but if I remembered I would shut off the fridge. And when on a ferry they shut off the gas to contain the propane if a fire was to happen. But trust me I seen a cabin burn and watched 3 100 pound propane bottles vent off and even though the bottle does not explode the venting sends off a big ass flame. That's why they have the new propane bottles that if there is a pressure differance they will shut down.
I hope this helps you and maybe all the professionals here will take note that running with propane on will be fine and propane does not start a gas station fire it's the ignition from the fridge that could cause this.