Raw steel needs about ten minutes of attention a year. Here's all of it.
It'll rust, and that's fine. Bare steel goes orange within weeks outside and settles into a stable dark brown within a season. It's surface oxidation, not corrosion through the metal, and on 2mm steel it makes no meaningful difference to how long the thing lasts. If you want to slow it down, keep the bowl covered or turned over when it's not in use, because standing water does the damage, not weather.
Seasoning a cooking surface. Wipe the plate clean and dry, rub a thin film of high smoke point oil over the whole thing, edges and underside included, and heat it until the oil stops smoking. Let it cool and do it again, two or three times before the first cook. After each cook, scrape it while it's warm, wipe it, and oil it thinly. Thin is the word: a thick coat goes sticky instead of hard.
Ash. Empty it when it's completely cold, which takes longer than you'd think. Ash left in the bowl holds water against the steel and rusts it faster than rain ever will. Wood ash is fine on the compost in small doses. Ash from painted or treated timber isn't, so don't burn those in the first place.
Winter. Nothing needs to come indoors. Turn bowls over or fit the lid so they don't fill with water and freeze. Fold the tripod into the shed. Keep a cover on the stove.