Surprised you do not have them. I thought they were standard, but I have been wrong before. I can only guess the venting occurs due to the "breathing" related to the heating and cooling of the roof/attic area during the day/night. Seems the attic insulation might absorb moisture from the inside over time if there were no venting at all. Maybe not.
Here is what they look like under that mushroom cap. Notice they have an extra "lip" that goes toward the front to keep rain water from blowing under when driving.
https://www.ebay.com/i/292080496866?chn=ps