My old boat had a Sharkskin cover. Cheaper alternative to Sunbrella. While it was 99% a dust cover in the shop, the times it did get rained on it was pretty waterproof. Never tested the UV resistance as the boat was stored indoors, but seemed like a good value and more waterproof than the OE MC covers.
'06 X2 MCX
"I understand why some people may not want to do this the way I have recommended but I can't understand the death grip some people have on a toilet plunger with a hose fitting." -JimN