Double Glazed Windows, Doors and Sliding Doors Manufacturer in Devon. M&S Windows Manufacturing Windows, Doors and Sliding Doors in Devon for 25 years.. Our focus now is on manufacturing, rather than instillations. We supply Windows, Doors & Sliding Doors to windows fitters, builders, DIY enthusiasts and more. We also offer a range of marketing and sales support services to regular customers. We are happy to assist you with your websites, social media accounts, SEO and any other area of sales and marketing.