If a person is always travelling, can he avail himself of the concessions of travel?
Question

We are workers for a Tunisian shipping company. We travel from Tunisia to Italy, and we go back to Tunisia, then on the same day we travel to France. We have one day off every week, and we stay on this schedule for 3 or 4 months.
Does the ruling on the traveller, allowing one to shorten prayers and put them together, apply to us?
When we go back to Tunisia and are waiting for the ship to travel on the same day (the waiting period is about four hours), does the ruling on the traveller apply to us during that period?
Please note that there are some workers who live near the port.
On our day off, there are some who do not go to their homes, because they are far away. Does the ruling on the traveller apply in this case?
If we do come under the ruling on travellers, can we shorten our prayers on the way to the ship?
Praise be to Allah.Firstly: 
With regard to the traveller who is constantly travelling, such as sailors on board ships, train drivers, taxi drivers and pilots, they may avail themselves of the concessions for travelling whilst they are actually travelling, but when they reach the place where they live, they must offer their prayers in full, because the description of traveller has ceased to apply to them. They must also – according to the view of the majority – offer their prayers in full when they halt in some city and intend to stay there for four days or more. 
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: 
He should break the fast (and shorten the prayer) – this refers to the one who usually travels, if he has a home that he returns to, such as a merchant who brings food and other items, and such as the muleteer who takes his mounts to bring merchandise (for a trader), and so on, and like the official courier who travels in the interests of the Muslims, and others like them. The same applies to the sailor who has a place on land where he lives. As for the one who has his wife with him on board the ship and has everything he needs with him and is always travelling, he should not shorten his prayers or break the fast.
End quote from Majmoo‘ al-Fataawa (25/213) 
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him) was asked: What about the man who is always travelling, such as if he is a driver who goes between cities? Is it better for him to shorten the prayers or offer them in full? And, by the same token, the other concessions that are allowed when travelling? 
He (may Allah have mercy on him) replied:
With regard to the traveller who is always travelling, such as a taxi driver or camel driver, if he is travelling by camel, as in the past, he may shorten his prayers for the duration of the trip, and he may put his prayers together for the duration of the trip. But when he reaches his city he should not shorten his prayers or put them together, and when he reaches a city where he intends to stay for more than four days, he should not shorten his prayers or put them together. But so long as he is travelling, or comes under the rulings on travelling, or the nature of his work involves travelling, or he is always travelling, then he is may avail himself of the concessions of travels, based on the texts of the Qur’an and Sunnah, as both of them classify him as a traveller. If a person is always travelling, because he is a camel driver or a taxi driver, he may shorten his prayers whilst he is travelling, and for the duration of his stay in a city he is passing through, if his stay will be four days or less.
End quote from Fataawa Noor ‘ala ad-Darb. 
http://www.alifta.net/Fatawa/FatawaChapters.aspx?View=Page&PageID=3375&PageNo=1&BookID=5 
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
Shortening the prayer is connected to travel; so long as a person is travelling, it is prescribed for him to shorten his prayers, whether he travels rarely or all the time, if he has a hometown to which he returns and knows that it is his hometown. Based on that, it is permissible for a truck driver to avail himself of the concessions of travel with regard to shortening the prayer, wiping over the khuffayn for three days and nights, breaking the fast in Ramadan, and other concessions of travel. 
End quote from Majmoo‘ Fataawa Ibn ‘Uthaymeen (15/264) 
Based on that, you may avail yourselves of the concessions of travel in two cases:
When you are travelling to the two countries mentioned in your question
and when you are staying in that place for less than four days, according to the view of the majority. 
For more information, please see the answer to question no. 105844 . 
Secondly: 
With regard to shortening your prayer in the port, that depends: 
1.
If the person who is working for the company is resident in another city, other than the city where the port is, then he also comes under the ruling on travellers, and it makes no difference in his case whether the port is in his country or in another country; what matters is his place of residence. 
2.
If he is a resident in the same city, and the port is within the boundaries of the built-up area of the city, then when he reaches the port, he is no longer under the ruling on travel, so it is not permissible for him to avail himself of the concessions of travel. So he cannot shorten his prayers or put them together, or break the fast of Ramadan. 
If he is setting out on his journey, it is not permissible for him to avail himself of any of those concessions so long as he is still in the port. Rather he may begin to avail himself of those concessions when he has left the built-up area of the city in which he resides. 
3.
If he lives in the same city where the port is, but the port is outside the built-up area of the city, and is not attached to the residential areas, then in his case the rulings on travel do not cease to be in effect just because he reached the port; rather he may continue to avail himself of the concessions of travel until he reaches the edge of the built-up areas of the city. 
But if he is setting out on his journey, then he may begin to avail himself of the concessions of travel when he passes beyond the built-up area of his city, even if he is in the port or someplace before that. 
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: If a person is in al-Qaseem and goes out to the airport, can he shorten his prayers in the airport? 
He replied:
Yes he can shorten his prayers, because he has passed beyond the built-up area of his town. All the towns that are around the airport are separate from it. But if he is one of those who live in the area near the airport, then he cannot shorten his prayers in the airport, because he has not yet left the built-up areas of his town. 
End quote from ash-Sharh al-Mumti‘ (4/364) 
And Allah knows best.