Hi Richard,
Just to confirm what Val has said about taking gas bottles on the Eurotunnel. It's not a problem, you might also read on the Eurotunnel website that gas bottles must be no more than a certain percentage full (think it might be 85% ) again don't worry about that as a "full" gas bottle is only filled to that level anyway.
We travelled by eurotunnel last year for the first time, definitely the way to go. On the outward journey someone checked that our gas bottles were turned off, nobody checked on return leg.
Robert