I just bought a custom fit cover from www.skiboatcovers.com
It's made out of sunbrella, has three support poles, custom tower cutouts and a nylon strap and buckle system that tightens the cover just below the rub rail.
It fits perfect and looks awesome. The Sunbrella material was important to me because it breathes much better than any other cover material.
I store my boat indoors less than a mile from the launch ramp, so I don't have a lot of towing distance between the water and storage for the boat to dry out.
The cover cost me right at $1000, but should last me well over 10 years, so that's really only $100 per year to keep the boat clean and dry... Small investment compared to the cost of the boat.