Great Lakes Boat Top makes the factory covers for Moomba and many other manufacturers. I'm very happy with mine. I was curious how much they cost so I got a quote for my 23' XLV and it would be $895 less a 15% off sale they're having through June 11th.

They are made with a waterproof/breathable fabric. mine has two built in vents and two poles. It has nylon webbing for cinching it up and gets tight enough to tow with the cover on.

Here's mine after driving 3 days across the country with plenty of rain. worked great.