In my experience most all machine tools will have a bare steel bearing surface, paint and other coating will last no time at all.
Just keeping them clean and an occasional very light oiling (you don’t really need lubrication/lubricity, just a film to keep oxygen out) will keep them rust free.
Believe it or not, out of the many products available regular old 3 in 1 oil is actually a pretty awesome anti corrosion coating.
This could save you time and money that could go toward something else, but I would think if you want to paint anything suitable for metal will do, the bearings will wear through the paint almost straight away, so you will only be covering the unused section of pipe.
On top of regular cleaning and maintenance I don’t think you will have corrosion issues.