I agree you should clear coat it. I didnt and my silver bubble still looks good 18 months later, but I keep it garaged and if you do clean it, just blot it like said before.
The argent has a very rough finish that will catch dirt easily.
If you are starting with an unpainted fibergalss bubble I think base prep should be no different than usual. Sand, fill, sand, prime, and then spray. Several light coats in different directions to get even application, esp if applying from a rattle can. If its already textured, you should sand it all off to start, esp if it has rough/smooth patches in it. That way you start with an even base. Otherwise it will look splotchy.
When I rattle canned mine, it was clean and uniform looking, but blah. I just sprayed several coats over the existing finish, and it sparkles new now. Looks much better now, though most others I see look to have a slightly darker tint. I'm sure thats from the clearcoat, which mine doesnt have.