135:17 If a person is distressed, he is exempt from the mitzvah of succah at night after the first night(s) of yom tov and on all the days. This applies to one who is distressed because of such things as the cold, the wind, a bad smell, and similar things. It would also apply to one who is distressed because the lights in his succah went out on Shabbos (when they can’t be relit) and going to a friend’s succah would be a lot of trouble. Such a person may go in his house where there are lights. This only applies if he built the succah properly and some situation came about that caused him to be distressed by eating or sleeping in the succah. However, if he initially he built his succah in the place of a bad smell or in a place where he is afraid to sleep, he does not fulfill the obligation even by eating there during the day. (If he’s not afraid of physical injury, just of theft, then he would fulfill his obligation because he could always just move his possessions from the succah to the house – Mishnah Brurah 640:19.) If the wind threatens to blow out the candles through the succah walls, one is permitted to spread out a sheet or garment to protect against this.
135:18 Those on a journey by day are exempt from eating in a succah during the day because they don’t have time to look for a succah and they need to keep traveling. However, if they are able to eat in a succah without difficulty, they are obligated to do so. At night time, when one is at an inn where he wants to sleep, he must make the effort to find a succah. If he is in a place where there is no succah, if he can make a succah at a small expense, he is obligated to attempt to have a succah to sleep in. (Mishnah Brurah 640:42 disagrees and does not require one to build a succah.) One who travels also by night has the same laws as by day. Those who travel out of town on chol hamoed to collect their debts, if they can’t make a succah, they should be stringent on themselves and return home each night to fulfill the mitzvah of succah. (They are only potentially exempt if they are traveling from village to village; if they are staying in one village for a few days, they are obligated – MB 640:45.)