I have owned many boats and covers. Sunbrella IS the best material. Whatever the material for the cover is, the flapping while driving down the road will be very hard on it. We took my Correct Craft Nautique camping a lot around the Western United States and typically the boat always held mass amounts of gear, so the Sunbrella cover was used while towing. It had mass amounts of tie down points (No bungee around the gunnel though) and I sewed up 1" webbing straps with a loop and quick connectors on the cover. The loop gets passed around the trailer, the connector passes thru the hole of the webbing and then clicked into the cover. Always stick them back where they came from immediately as they are set lengths that will rarely need to be adjusted.
For outdoor storage I've always used a rope down the middle with a center support or two. The custom tower I had in my wakeboard boat folded completely into the boat supported by a wooden rack and it slightly pushed up on the cover, but a center pole of ABS pipe was still needed to form a tent. I'd often check it after heavy rains and if ever a drip inside it was washed in an industrial machine, then put through another cycle with a couple bottles of Nikwax to re-apply the DWR, followed by air drying. This wash cycle will leave the cover breathable. In the summer it kept the sun off and the critters out. *shrugs* A solar fan would be good to have and wouldn't be hard to build a plenum out of plastic, or wood.
You are not going to get the perfect boat cover fit unless you pay a lot of money, like double for a custom cover. Even then it will still need support to keep the puddles off it, the rain out; and a lot of tie down points for towing down the road...or so my experience has shown.
Oh and my well worn Zodiac cover tore while towing. Iron on patches happen to work really well for keeping an old cover functioning, but even better is Aquaseal thinned with Cotol 240, applied to the break, and put a second layer of material over the tear. Just a stronger bond, then iron on patches. Iron on patches are faster and cleaner since there is no messy glue.
Best to fully explain what you are looking for in the original post that way folks can offer more specific answers. Good luck on your search
That is effectively your boat right? Larger boat covers makers use CNC cutters and programs to cut out a semi fitting boat cover based on manufacturers dimensions with usually a little extra. I've found it best to run a rope from bow to stern or onto the trailer at either end. A post or two mid span makes the loose cut fabric into a nice ^ to shed rain.
