People are afraid of LPG or any king of gas. Dont know why but I've met many who claim to rather have just electric supply than gas.
This is the result of lobbying and the spreading of paranoia by the various gas-related trade organisations to promote their "jobs for the boys".
Gas is just like any liquid / gaseous substance - liquid fuel, compressed air, even water, sewerage, etc..
Sealed = Good
Leaking = Bad
Nothing to be afraid of, really.
Yes, there are invisible dangers associated with its' leaking. Just the same as there are with petrol vapours, or even Methane from waste.
I would have thought there'd be a similar issue with any potential gas spillage accumulating in the bilges of a ferry but maybe they are properly ventilated?
As you say the channel tunnel has been built and is running on a shoestring. Last time I tried to use it it was a total farce due to the cables having fallen down onto a train - so I won't be repeating that experience all the while London has an airport and Dover has a ferry port!
Kevin