I use ph neutral soap to wash everything since things are ceramic coated. I would test a small spot using foam cannon car wash soap and make sure it doesn't hurt the cover.

If all good, leave the cover on the boat and foam cannon the whole thing and use a delicate power washer tip to rinse. Leave in the sun to dry.

I have the older Moomba cover (gray) and this has worked for me evey spring. Once the cover isn't gross from the barn/shop, I remove and start the boat cleaning. Cover is still water resistant. Drove through soaking rain down to Norris and had to stop to get the puddle out of the bow. Boat was wet but the cover held a puddle so water repellent is intact.