Reply by bigblockyeti

It would be expensive, but you can have two part foam insulation sprayed right over the metal as is, or you can clean some of the rust off a bit before having it sprayed. It would keep condensation from being able to form on the metal and wouldn’t add much dimension to the ceiling cutting down on your head room. Sanding the rust off the metal could be accomplished efficiently with a grit in the 60 – 80 area.

-- "Lack of effort will result in failure with amazing predictability" - Me