Yosef Karo

“ Even if one is just traveling during the day, they are exempt even at night because they cannot make a dwellingplace there. Those who go to villages to collect debts who do not have a sukkah in those villages should be stringent on themselves to return to their houses each night to eat in the sukkah. ”

“ Those who guard the city at night are exempt at night and obligated during the day.
סעיף ט
שומרי העיר ביום פטורים ביום וחייבים בלילה שומרי העיר בלילה פטורים בלילה וחייבים ביום:
640:10 Those who guard fields and orchards are exempt both during the day and at night, because if the guard makes a sukkah, the thief will know that they have a set place and will steal from someplace else. Therefore, if somebody is guarding a collection of crops that can all be kept in one place, he is obligated in the place that they are kept. ”