Regular Fantastik (no bleach) is recommended by one of the largest suppliers of marine vinyl. I've used it for years with great results and no adverse effects. I then follow up with Meguire's Marine Vinyl Cleaner/Conditioner. I used the magic erasers last year for the first time on some trouble spots and they too work great.

We also use fantstik to clean every boat in our inventory....have not had any problems....it will also work on fiberglass in a pinch.