Re: Carrying a propane tank inside the van while traveling.
I have seen a video, as part of my lifetime ago propane training, that showed a bullet piercing a propane tank. The propane leaked out as a liquid, vapourized, and that was that. No flame, no explosion.
These tanks are built and certified to an engineered standard and tested.
Now let's review the fuel tank hanging off the back end of your van between your rear axle and rear bumper. It is sheet metal or plastic and believe it or not receives no certification or independent testing.
If it contains gasoline or you carry a gasoline jerry can I would be infinitely more worried about the gasoline igniting than I ever would be about the propane doing the same thing.
A diesel tank, as my grandfather attested from his war time experience, is a lot harder to ignite.
My conclusion is to secure the propane tank and worry more about the clown behind you texting and not paying attention as he plows into you, pierces your built-to-no-standard plastic tank and ignites the whole thing.
Maybe the weight of these things is an advantage after all.
"Talk is cheap. Whiskey costs money."