General upholstery shops can sew a cover. Marine canvas specialists design one to survive the specific conditions your boat actually lives in.
We work with marine-grade materials every day: Sunbrella (industry standard, solution-dyed acrylic), Stamoid (premium PVC-coated polyester for maximum water resistance), Phifertex (breathable mesh for hot-weather seats), Sunbrella Horizon marine vinyl (UV and microbial-pinking resistant for seats and cushions), and marine-grade thread, zippers, and hardware throughout.
And we know where each one fits. Sunbrella weight choice for a moored boat versus a trailered one. Frame geometry that won't flutter at 30 knots. Seam placement that sheds water instead of trapping it. The things that take a cover from "looks good on day one" to "looks good five seasons in."