All of the above can be protected by a wax, polymer sealant, ceramic coating, or similar product. Bare Aluminum will pit and corrode without protection and the Anodized Coating will be destroyed without protection, leading to corroded aluminum. Stainless is a little easier to buff and clean up, but still needs protection.
Pro Polish is a polymer synthetic sealant designed to chemically bond with the surface it's protecting. It works on almost any no porous surface, in your case gelcoat, paint, and metals. Wipe on, wipe off protection for a few months.
Ceramic Coatings are very cool tech, but the application process is crucial to their performance. Working on a piece of pipe would be tough. There is also the cost to consider. Most reputable ceramic coatings will cost serious $$. Can it be done? Sure. I prefer waxing, IMO