The concern while re fueling is kind of potentially a concern. The exact right conditions at a gas station "could" light off gasoline fumes from a fridge flame. Very low odds of that unless you spray gas at the side of the camper!
An open propane bottle while driving down the road is not.
There are lng powered vehicles everywhere. All gasoline cars are also extremely flammable in the wrong situation. As well, when a propane bottle starts running out gas unchecked, the check valve closes. So short of punching a hole in the cylinder or knocking the valve off the top they are as safe in use or not while traveling.
And for those that don't get out much, very few car crashes end up in fiery explosions like EVERY one you see on a tv show....