303 Fabric Protector works well, but as stated you can't let water pool on the cover or it will leak.
An alternative is to cover the boat with your normal cover, get a silver tarp (higher grade than blue), build a "tent" using PVC pipes...run one from the windshield to the stern with extensions that come off and rest on the gunnels. Then the same with the Bow, and throw the silver tarp over the "tent" set up and strap it down.
Does this make sense?
I have zero adobe skills and no pictures, sorry.
Another alternative, growing up, my dad used sheets of aluminum siding, bent them in the shape of an A-frame room, and threw the tarp over the top...same concept.