I got a custom made one from Eastside Tent and Awning in Bellevue when I had my 16 footer. The cover was made of sunbrella fabric and it custom fit my boat. Where I live we get a lot of wind and a lot of crap coming down from trees and a lot of rain and snow. This cover held up extraordinary well for 10 years and I sold it with the boat a month ago.

The sunbrella was more expensive then standard canvas, but if you are going to have the boat for a long time it is worth the extra expense. The custom fit allowed me to tow the boat covered with no flapping around. Before I got this cover I had a Cabellas cover that didn't hold up too long, nor could I tow with it on.
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"90% of Life is just showing up and doing the work". Tred Barta Sr.