[JRTJH]

All of the recent model Cougars and Cougar Half Tons that I've seen have a OEM drip rail over each silde. Most slide covers are sold with an awning rail insert provided in the kit.

There are three ways to install the awning rail. First, you can buy an optional "drip rail/awning rail" aluminum molding to replace the OEM drip rail and slide the slide cover awning into the new awning rail molding.

Second, you can install the provided awning rail that came with the kit "just below the existing drip rail"... I found that on my trailer, the OEM drip rail was where I needed to install the awning rail.

So, the third option: Remove the OEM drip rail, install the awning rail in its place (there's usually a backer strip in that location) and then reinstall the OEM drip rail above the awning rail. This is what I did, sort of "double protection" against water leaking into the awning rail seam should the slide cover pull it away from (or loosen it) the trailer wall.

As for the need for a "backer plate", many trailers have slide covers that are simply screwed into the FILON sidewall. Essentially, if you use BUTYL putty tape under the awning rail, the screws AND butyl putty tape will hold it securely whether it's in a backer plate or just in the FILON.