I painted mine with high temp automotive manifold paint inside and out several years ago, it's made with crcq raw steel and over the last 5 years the only thing that's rusted is the unpainted false floor. Every fall I haul it out, touch up any missing paint from bumps and bangs and do a slow burn in with charcoal to cure the paint- a $15 spray can is plenty to do touch-ups for years. I use the same on my pipes (cheap galvanized ducting with the coating burned off) and I finally had to replace a couple of elbows last year, not from rust but from getting crushed.