We use the power vent anytime we are cooking bacon. Other times it is optional. I am tempted to somehow connect the fan to the smoke detector so that it turns on automatically.
We only have two vents. The other one is in the center in front of the a/c. This one is critical for the TM. Where else would they hide the switch for the front reading lights.
This vent is open all of the time if it is warm out.
We have no reason to open the vents in the rain because we rarely camp in the rain. That is why our camping season is limited to May 1 through October 31. (I enjoy rubbing this in)