Talked to my dad about this one (retired chemist and plating nut), and he says the rubberized coatings and non-metalized coatings will only serve to ACCELERATE the rust as it traps the moisture in-place along with any minerals which may be part of the problem. You would have to remove all traces of rust using acid before applying the coat.
Cold galvanization is absolutely the best bet in your case, as that will absolutely stop the rust. The only thing better is true zinc plating using zinc salts and some decent electrical current at low voltages. The zinc becomes a sacrificial anode (yes like a battery), and it provides the corrosive surface rather than the pipe. Zinc is fairly resistant to corrosion as well.
I have a can of the cold galvanization spray I have used on various projects and it really works well. I used to use the aluminum spray as a rust inhibitor, but the zinc-based products work a lot better. The spray I have is "industrial", I can get the brand name if you wish.
