Before the marina hauls and winterizes your boat, there are many jobs that you, the boat owner, can perform. Most marinas will look after the motors and water systems, but they won’t do some of these more detailed jobs.
Protect your cushions and mattresses
If your cockpit upholstery has been damp during the last few weeks, lift it up off the seat foundations, stand it on end, drain it, expose to the sun and the wind. If your upholstery is going to stay aboard after haul out, go back to the boat after the marina has finished winterizing it to stand the cushions and mattresses on their side and lean them separately against the cockpit sides. This will provide good ventilation around them. There are always lots of warm days during the fall that will draw the moisture out of them, if there is good air circulation.
Clean before storing
Fall is a good time to wash just about everything on the boat--inside and out so that you don’t have frozen on dirt to deal with in the spring. This job includes washing the canvas, the upholstery, the superstructure, coolers, the frig, ice maker, lockers, live wells, bait wells, etc. Also, this will avoid black fur in the corners greeting you in the spring.
Brush Away the Mold
This tip I was given for black mold that forms during the fall on the underside of convertible top canvas.
When dry, remove the canvas from the bows, spread it out on a flat surface like a piece of plywood on a picnic table. Next, put on a handyman's paper face mask, so you don't inhale the mold dust. Brush away the mold with a dry scrub brush. Use no water, no cleaners, just brush dry. Brush parallel to fabric "grain" to loosen mold from the weave of the material. Shake like a bed sheet in the wind. Repeat brushing as required on corners missed. Brushing dry does not wash out the waterproofing.
Hang to Store
Depending on your storage space at home versus your varmint problem on the boat, you may also want to remove your convertible top/bimini top and all the canvas. One winter, I had rolled up the tops super tight around the bows after washing and drying thoroughly. Come spring, when I unrolled them, a family of four-legged critters had crawled in the rolled up end with some paper and made a cozy nest. Nest creation involved chewing several holes in the rolled up canvas. Every year since, I hang the canvas flat like sheets on a clothes line in my storage shed, so that there are no pockets to nest in.