well the ONLY sure fix is panel replacement...$$$
there is NO replacement product compatible with the alcoa coating,
beyond the treatment of tiny spots with nail polish or auto clear touch up...
so PLEASE post photos...
it is hard to believe patches of the alcoa clearcoat are missing on a 4 year old trailer.
let's SEE what is going on with your unit's finish...
are there any patches of corrosion anyplace?
all of the true things that i am about to tell you are shameless lies. l.b.j.
we are here on earth to fart around. don't let anybody tell you any different. k.v.