I think folk get a bit worked up about this for no good reason. It is only the fumes that are dangerous and as long as you are sensible and ensure the containers are well sealed there should be a problem. Obviously this is for the odd 20L can and not whole vans worth of plastic bottles!
Think back to the Glasgow Airport attack, this was a vehicle loaded with fuel and run into a door and set on fire, it didn't explode!
A little bit of common sense and good ventilation is all that is really required and if you think that you are on a death defying roller coaster ride that may result in instant death at any time driving a few miles home with a 5l plastic jerry can full of petrol in the car then maybe you really need to go and lie down in a dark room for a little while.