For the vinyl after cleaning apply car dashboard protective spray, which is also sold as clear tyre shine spray. Cheap, and a good source of plasticiser for the vinyl, as you find vehicle interior plastics also use the same vinyl, which loses flexibility with age. Spray on, leave for a few minutes then wipe off, and place the cover where it will be flat and unwrinkled, for a few hours to have the placticiser soak in evenly.
I bought a 5l bottle of it around 20 years ago, and used it always on plastic vehicle trim, and this definitely has helped preserve them. Note that it is a dust magnet for a few days, till it has soaked into the vinyl.