These screw covers on the channel serve several purposes. First is the cosmetic the camper looks better with them in place. Second they help to keep water from making its way around the screws and therefore into the walls of the camper causing rot.
These are vinel strips and are easy to replace. You can get them from most rv dealers or on line. If I remember they only come in a couple of width so you will have to measure the width of the channel. They also come is several colors so just match to the existing.
Chuck & Sandra
2010 F350 CC 6.4
2015 Prime Time Sanibel 3601