One important item is that the boat interior needs to "breathe" under the cover to dissipate vapour. Gas goes out the gas cap breathers or just what's lying around in the bilge and with the heat rises to attack the windshield, instrument covers and other acrylic pieces, causing them to craze.
If the fabric doesn't breathe, make sure that you put in grills to get some air flow going under the covers.
Also if the cover contacts an acrylic windshield be sure to have a softer material sewn on the underside.

call carrie covers. great covers lightwieght and great prices too

Top Gun works great up north to keep the snow and water off, but doesn't breathe very well and tends to mold the interior of the boat in the humidity and heat. Sunbrella or the newer frabics in the heat.