Sometimes the ends don’t justify the means, though.
There’s a better way than snooping… try communicating with him more openly. Ask him questions and respect his point of view and thoughts. Having healthy, open discussions will breed trust and understanding… but sneaking around and snooping will only breed distrust and close him off from you even more.
Ask him! “Hey, I know this trip you’re taking is important to you… can you tell me why?”
And then LISTEN. Don’t interrupt, don’t question, don’t interpret… LISTEN.
The more openly you can communicate, the more he will trust you with his thoughts and feelings.
Or… if this trip is something you don’t want him to take - explain why and follow through on that. You’re the parent!