I'm very close to buying a CR21A Spectra fuel tank

I don't know what this means: "Ni-terne plated steel gas tank"

I'm concerned about the bare/bright finish of these things. has anyone used one of these tanks for several years? do they rust quick? is it worth scuffing and painting? Sure would be nice to have something bolt right in for $300.

Looking for 1975 through 1978 B body 4 door sedan sheet metal or parts cars - monaco, fury, coronet. Please let me know