Seasoning An Offset Smoker Season The Firebox Of My Offset Smoker?

Season the firebox of my offset smoker? - seasoning an offset smoker

I have served a New Braunfels offset smoker to me is good for the last seven years. But he was rusty, especially outside the fire area, and I sanded and painted with 1200 degree grill. The inside of the chimney is properly dried (fat) and does not corrode, but is dry inside the house and a little rust.
Has anyone experience (including oil) in the combustion chamber?