The Black Vinyl D Pillars are actually folded aluminium, covered in vinyl and bolted to the vehicle. The vents are to allow fresh air circulation into the vehicle. The do not allow direct access inside. If you were to remove them the vent on the body is further toward the top, with the vent on the D pillar at the bottom. I recovered my D pillars not so long ago and the bigger area of concern I would say is the mounting bolts themselves. these are fixed to the cover and pass through the bodywork into the car. I would remove the panels and have a look if you're concerned. Have you checked your boot area under the carpet and sound deadening for damp? If you want to remove the pillars its a simple process, removing the inner trim (and seatbelt inertia reel if fitted) to reveal 3 plastic caps covering the nuts (8mm If I recall) You will also need to remove the screws that sit in-line with the tailgate.