It was important to get a roof rack on our Sprinter Van. We looked at a lot of racks, we really wanted an Aluminess, but not enough money. So we got a factory roof rail and rack system.
I called the Mercedes Benz Sprinter dealer I purchased the van from and asked about how to install the roof rails. Matt was a service technician who helped me when I purchased the van, he was super helpful again. He told me that all I needed to do was remove the plastic grommets from the existing holes. He suggested a small torch and a screwdriver from below to remove the plugs.
It worked like a charm. I am looking for pictures now.