I don’t see a point seasoning the inside of a charcoal grill. I’ve seen folks on YouTube coating them with vegetable oil and then burning it off, which makes no sense to me. Vegetable oil has a smoke point of 400F. If I were to get the grill up to high heat to sear a steak, this ‘seasoning’ would just burn right off.
Instead, I keep the inside of my grills clean by washing them out every other cook or so with the garden hose, some Dawn soap and a plastic bristle dish brush. Takes 5 minutes and doesn’t have to be perfect, just mostly clean, or clean enough to avoid having a dumpster fire. Here’s my Jumbo Joe, I’ve done maybe 50 cooks on it and I bought it used.