redhead genesis 1100

What is the best method for patching rust damage on porcelain lid?

I was lucky enough to find a Redhead Genesis in really good condition. Everything was original, missing Flavorizer bars, rusted burner tubes (expected) I Dismantled the cook-box, hood and frame, sanded it down, sprayed it with Ultra High heat Semi Gloss. I wire brushed the burners but...