Important: These usages talk about amounts of time that pass. But the second and third seem like they try to talk about the length of time that the speaker spent travelling, while a construction using "since" is probably trying to talk about the length of time elapsed after travelling happened.
Let's take a simpler example. Let's say I was stuck in an elevator for an hour. This event happened a year ago. If I want to talk about the duration of time that I was in the elevator, the most likely option is "I was stuck in an elevator for an hour." I might also say, though this is less common and a bit archaic, "It was an hour that I was stuck in an elevator."
If I want to talk about how much time has passed since the incident, the most likely is "It has been a year since I got stuck in an elevator."
Now, in that sentence, the overall tense is present. If I want to use the same sentence in an overall past-tense narrative—for example, I want to look back not only on the elevator incident, but on the time that I told a story about it a year later, I might say: "That day, I told them about how I had been stuck in an elevator for an hour. It had been a year since I had gotten stuck (though more years have passed now)."
So don't confuse the tenses and the "since"/"for"/"that" usages. The past perfect tense is useful when we're already using past tense, but also looking back at something even earlier than the main time point of the sentence, so "had been" is best in that scenario. Meanwhile, "since" conveys time elapsed between an event and the main time point of the sentence, while "for" (or perhaps "that") are used for durations of time with beginning and end points.