How secure are these trains? Me and my wife have a double sleeper but if we both leave to eat in the dining car can you lock your room? If not how safe is your luggage?

This train has only overnight accommodation (sleepers and couchettes) and can only be used by people travelling to Italy. After Paris, I think the next stop is Dijon where people can join the train but not alight.
Your luggage will be quite safe in your sleeping compartment. You should obviously keep money and credit cards on you. The compartments can be locked from the insides, but passengers don't get keys. If you want to lock the compartment, ask the attendant who can lock it for you. Each carriage has an attendant who will collect tickets and passports after passengers board and return them in the morning (this is because the train passes through Switzerland and you won't need to be woken up if the Swiss police want to check passports).

Good advice from Geoff and more information here:

http://www.seat61.com/Italy.htm#The%...0to%20Italy%20...

We have taken this overnight train a few times. It is, as noted above, reasonably secure. My suggestion however relates to your proposed use of the Dining car. As I recall it's a long walk to that car and the prices are terrible. Since the first trip, I've always bought food and drink locally and consumed it in our sleeper.
Much more fun and relaxing than contending with the Dining Car. And nobody cares if you consume too much cheap wine.

Great info thanks, 2 more weeks to go
Ireland
Wales
England
France
Italy