Dear macabf,
The root cause of rusting/corrosion is oxidation. One route out is, to shut-off the oxidation process by putting up a barrier on the metallic surface of the tank. Paints, Red oxide widely used offer reasonable protection. But as Lamont rightly pointed out, chips/debris from paint will have detrimental effect on performance, as, in many of the sophisticated Hydraulic systems & FR Fluid systems, the fluid passes through very fine tolerance Moog valves and Servo valves.
You may like to try out new development in nanotechnology. Boron CLS Bond technology has an excellent offering, whose link is posted below:
https://www.evergreenamerica.c...t%20tech%20sheet.pdfHussam