is it dangerous to store propane on a frontrunner propane holder?

I recently purchased a front runner propane holder for my front runner slim line rack. I was told by the propane sales person that everyone just puts propane in the back of their cars, and says it's more dangerous to carry on the top as it could fall off and explode. What do people think? I don't often see people with propane on the top, so I'm a bit concerned. Thanks.

 

That guy might know propane and propane accessories but I don't think he knows roof racks and roof racks accessories.

 

Did he also tell you that the "Everyone" is Just running home to take it right back out to put it on their Barbeque Grill?

For long term travel on top is much better than inside, since inside with a leak can turn vehicle into a bomb! The only concern about on top is the weight can you without effort lift the canister up there and back down when it is full.