I never really thought about this before, but what in the world are the vents at the bottom of the door panel for. I been pondering this for a few days and i'm 'bout ready to pull my hair out. While I'm on the topic of door panels, has anyone used painted diamond plate as trim pieces on their interior? I was thinking about doing that at the bottom of the door panels where feet tend to bash them. That's when I began scratching my head about the vents.
You also need them to keep condensation from accumulating in the doors. I think it would be a bad idea to seal them up. Whenever you run your heater fan, you'll find air blows out the door handles outside. It's also venting through the vent in the end of the door below the latch. This airflow keeps the inside of the door drier and it's a good idea.
If you seal them up, it will severely cut down on the efficiency of your heat and A/C. Pushing fresh air in requires the old air to go somewhere. If you seal them up, it has very little other places to go and it will make the system over-work and not get much done.
Thanx for the feedback. I've never really given it much thought, but I have noticed dust collecting on them like a filter would. During the summer, I've felt the cold air flow from the handle on the outside. I suppose it would look tacky if I were to take a piece of alum. diamond plate and cut out a section for the vent. I am just thinking about changing the interior color and was thinking of a way to put something there that would stand up better to abuse than paint.