Abstract: A weatherproof sliding door assembly for opening and closing a boat cabin companionway wherein upper and lower aluminum track C-channel rails are supported to extend generally horizontally above and below the companionway. Each rail has a hollow interior slideway and a longitudinally extending slot opening thereto. A flexible plastic door panel has upper and lower edges respectively juxtaposed to the upper and lower rails and slidably mounted therein by upper and lower slide and cap panel-clamping sub-assemblies respectively that are secured by clamping to the door panel upper and lower edges and that extend the full length thereof. Each sub-assembly has a first leg wall extending therefrom into the associated rail slideway via the rail slot opening and terminating therein in a glide carrier portion. A pair of glides are mounted on each glide carrier portion adjacent its longitudinally opposite ends and bear slidably on the rail slideway for supporting the door panel for sliding motion along the rails.