Is it permissible for a person who constantly travels due to the nature of his work to refrain from fasting?

The dispensation for a traveler to break his fast

Allah Almighty permits a person who is traveling to break his fast on the following
conditions:
- The distance of the journey is not less than 83.5 km
- The purpose of the journey must not be an act of disobedience.

A legal ruling is determined according to the presence or absence of its cause The Shari'ah made travel a legitimate reason to miss one's fasts, irrespective of the hardship that is usually associated with traveling. Therefore, it is valid to consider traveling itself a manifest and regulated cause ['illa] upon which to base the ruling.

A ruling is dependent upon the presence or absence of its cause. Therefore, a person who is traveling is granted the dispensation to miss his fast. As for the hardship associated with travel, it is unregulated because it differs from one person to another, and therefore it is not valid to base a ruling on it. For this reason, the ruling for the permissibility of breaking one's fast while traveling is not contingent upon the presence or absence of hardship.

Allah Almighty says, And anyone who is ill or on a journey should make up for the missed days by fasting on other days later. Allah wants ease for you, not hardship.
[Qur'an 2: 185]
So when a fasting person is traveling, as long as the purpose of the journey is not to disobey Allah, it is permissible for the traveler to break his fast whether or not his journey involves hardship or the travel is constant. This dispensation is applicable even if his constant traveling is a result of work-related responsibilities.

It is better to fast

Allah Almighty made it clear that, in spite of the dispensation to miss one's fast, it is better for a person who is traveling to fast. He says:

And fasting is better for you.
[Qur'an 2:184]

It is better for a person who is traveling to fast as long as fasting does not pose a difficulty for him and he will be rewarded abundantly. This is because fasting during Ramadan, for those who are able to, outweighs fasting at any other time. If a traveler believes that fasting may harm him, it is disliked for him to fast and if he fears death, it is obligatory for him to break his fast.
Allah Almighty knows best.