If you have a propane cooker large enough to get it hot that is what I would do. Yes you want to season the inside and out. If you can do it with your cooker I would heat it at 350 (give or take) for about an hour. Then crank it up a little warmer for another half hour or so, then let it cool naturally.
If you have to do it over a fire I would build a fire and let it burn to get a hot bed of coals. Once the flames die down and you just have the coals I would oil it up and then put it over the coals. That might help keep the soot down and still get it hot.