Framesaver works. I believe the spray / material was developed for and used by the US Navy. I would treat the frame prior to building it up and then periodically re apply to your seat tube ( 1 or 2x / year) which tends to be a problem area for steel frames (condensation / moisture forming and dripping down the inside of the seat tube). Follow the directions and rotate the frame and invert with a rag stuffed in the top of the tube to get the framesaver covering the entire inside of the seat tube.
Nasty stuff though. Apply outside if possible (good ventilation) and wear eye protection and gloves when applying. If you maintain your CrMo frame with frame saver it will last a very long time.
Good luck - Steel is real!