No, the rear vents should be okay. They allow air to flow through the cabin. On the inside pillar at the back you'll see the outlets.
Pull the carpet back just along the top edge along the firewall. From one side to another, and if you find where it is damp, then directly above might be where it...
Its a bit of a pain in the a..., but sometimes crap piles up around the air intake for the heater above the cowl and firewall.
If you unbolt the wiper motor, pull it out, then get a flashlight and look to the left and see if the metal screen is piled high with
leaves, pine needles and stuff. If...