My Old Country Brazos offset is real quarter inch (rolled) steel and has set uncovered outside on the patio for the 14 months since I bought it. After the first couple of cooks, the firebox started to rust a bit so I bought some Ospho (after asking advice on this forum). Wire brushed the rusty areas and applied the Ospho according to directions. Painted over the treated areas with high heat paint and haven't seen a spot of rust since.
BBQ Apprentice - Old Country Brazos offset, 22.5 WSM, Various gassers, portable grills, etc.