The main function of RV trim end caps is to end the flat trim piece cleanly. The end cap slips onto the trim and is screwed into place, securing the end cap, the vinyl insert, and the flat trim.
The extra protection provided by the end cap extends the life of both the trim and the vinyl insert, protecting the vulnerable ends from water and the sun, both of which can hurt the trim and the insert over time.
The end caps are made of powder-coated aluminum which means it's light but durable. The powder-coating is also terrific for an exterior piece. Unlike traditional paint, powder-coating is made for those pieces that go through a lot, such as RV trim.