It all depends on the year of your truck, you either have a metal bedside rail (older trucks) or you have plastic caps (newer trucks).
With the increased demand for vehicles to have better fuel economy, automotive manufactures continue to make automobiles using thinner and lighter materials. One of the drawbacks of doing this is the loss of durability. In order to compensate for this automobile manufactures are adding corrugation to top of the rail which gives it structural integrity, this however looks unsightly. So in order to cover up the structural corrugation under the rail, they top it off with a replaceable plastic rail caps which cost approximately $250 for a 3-piece set.
The rail caps have plastic clips cast into them which when removed tend to break. This will lead to the cap lifting up slightly. Although it’s uncommon, we have had customers request that we spray under the caps as seen in the photo below. Normally this is done because the customer intends on leaning items against the bed and they want the paint protected. Older trucks on the other hand don’t have this issue as they have solid metal bedsides.
Most of our customers who bring us older trucks have us spray over the rail. This not only protects the bedside top but can hide previous damage. Our technicians take the time to do this right, we ensure that your rail line is perfectly straight and level.