The boat cover has been used for 15 years worth of Seattle rainy winters. It goes on around November 1 and comes off by mid to late April. The cover was custom made using marine canvas (Sunbrella) with zippers and twist locks connecting 4 large sections. I usually rinse it with a hose, allow it to dry, and pack it inside 2 huge duffel bags, then store it in a garage until bringing it back out for the winter. Over the years it has accumulated quite a bit of dirt and mildew, so this year I decided to clean it well. I started with a hose and a canvas cleaning product, lightly scrubbing it with a soft brush and then rinsing. This did very little in the way of making it look any cleaner. So I decided to bring out pressure washer and that made a huge difference. It took a few hours of spraying at close range to remove most of the grime, but it came out looking almost new. After drying well, I applied 3 gallons of 303 Marine/Aerospace protectant using a garden sprayer. This gives it UV protection, and makes it water repellent and stain resistant. I also cleaned and treated the 18 canvas bags that hold sand used as weights that clip on along the bottom of the cover.