Depends where you are touring. The only time I had any problems was in the countryside where youths with nothing to do attempted to steal my sister's bike which I'd parked outside a shop in full sight leaning against the window. (Learning #2 - don't borrow your sister's bike when you have a puncture).
- when we eat lunch we leave the bike in sight with the brakes adjusted so that you can't ride it off immediately. No problems so far. Alternatively the chain can be derailed, but I don't like doing that.
- Otherwise we don't leave the bike unattended unless it goes in someone's garage or locked room. Most places we've visited are happy to help if you ask in advance. If they can't help we go somewhere else.
If I had to leave the bike unattended I would remove the front wheel and lock that plus the frame and rear wheel to an immovable object. I have a motorbike chain and Abus Disklock for that sort of thing, but it's so heavy I wouldn't want to carry it around unless travelling by car.
To simplify things you could use splined bolts to fix seat posts and wheels, then you would only need a small D-lock for the frame. That would be 90% secure, but would not protect against vandalism, hacksawing the frame to get it out of the D-lock for the components or allen key wielding thieves stealing the stoker bars etc.