Huge fan of 303 - goes on everything, cars, bikes, rv, anything with wheels.
I learned about it when I bought an inflatable boat a number of years ago. They said not only does it work well to protect the hypalon fabric of the boat but is the only protectant that will allow you to patch it. Any silicon applied can never be gotten completely out of the rubber and prevents a patch from adhering.
Now I just use it on everything inside and outside. A quart lasts me a couple of months, usually buy it at West Marine. Online retailers offer it a couple of bucks cheaper so if you're ordering other detail supplies anyway there's some savings there.