Hi,
1. Would you say the use of the indefinite article "a" is meant to give a more remote sense of the phrase underlined than were it used the definite article "the"?
That night he had a vision of a woman going up the mountain to pick some plants.
2. Would you say the indefinite article "a" is additionally modifying the word "vehicle" and "activity"?
*** is a person who goes from place to place living in a car or other vehicle.
They write what they think following a reading or other activity.