Rather than epoxying the inside rail, I recommend using a forester bit to over drill the inside mounting holes without penetrating the outer skin. Then tape up the holes and use a syringe with thickened epoxy to fill the holes. The cured epoxy can be drilled and tapped with appropriate SS fasteners to attach the inside rails. Use bungs to cover the screws but don't use glue so they can be removed when desired. Sand the bungs to match the profile of the handle and use a good marine polyurethane to seal everything.