Back in 2002 Manchester had problems with their paint process. I think shortly after they went to powder coating. Mine, when new, had so much rust I made them replaced it with one that was powder coated. I figured if it looked that bad then I didn't want to have problems years later.
If it's just surface rust not a problem, just cosmetic, but if the metal is being eaten away, I would remove it, strip it, get all the rust off, prime, and spray paint it with a good metal paint.
Not hard to remove the tank, but much easier on a lift. I pulled mine, because I could faintly smell gas. I could not find the leak, figured it had to be somewhere behind the tank, sure enough a compression fitting had a crack in it. About a 2 hr job, and a couple bucks for the fitting. You are dealing with gas lines, so if your not comfortable removing, and reinstalling the tank yourself have a RV dealer do it.