Even though once before a moderator deleted some of my posts which contained safety comments about battery boxes (complete with references) because some other member's replies were over the top... it seems that some here are questioning my ability to understand systems, so I'll reply here.
Anyone who has any safety training should know that the fire triangle has three elements. Oxygen, fuel, ignition (heat). If all three are present there is danger, take away any one and the danger is gone.
We live and drive in about 21% oxygen. So no control over that.
We pull into a fuel station and EXPECT that conditions will be normal, but there may be a fuel spill or other problem which we have no control over. So not much control over that other than avoidance should you observe something as you approach.
Ignition source. Now there's one we can control. We can not smoke cigarettes around fuel stations. We can shut off our engines. We can make certain that our trailer doesn't have an open flame by not running propane appliances.
Some people think it is silly to pull into the station and then go back and shut off their refrigerator. I agree completely. It should be done before you get to the fuel pump area. Nobody can convince me that if they want to operate their propane appliances while on the road and also fuel up safely, that there isn't somewhere in the parking lot to stop, turn off the appliances and THEN proceed to the fuel area. The same applies to tunnels. There is plenty of signage and warning for anyone who really cares about safety to find a safe place to pull off the highway and secure their propane tanks before the tunnel.
A vehicle with an engine running pulling up to a fuel pump presents little risk. The engine fan is moving air across any potential spark making or heat devices which keeps the atmosphere out of an explosive range. In fact, with electronic controls there are fewer spark making devices in a vehicle anymore anyway. So pulling up and driving away do not present a big risk.
As to fuel trucks... last time I recall being around them they are storage and transport trailers. They do not have any open flame appliances associated with them. There are however many regulations and rules specified by the DOT for proper operation of fuel transport. They are not at all the same as pulling up to a fuel station with a travel trailer which has an operating open flame.
Threebutchers has the right idea. It isn't the normal conditions which will get you. It is the abnormal, unexpected which will be the problem. You will not be able to pull your strapped in the back seat, burning grandchildren out of the fire in time once your trailer has sparked some spilled fuel vapors. Most tunnels have no escape.
Do with my opinions what you will. vic