I have mine doing the initial burn-in now. I'm using Pan cooking spray on the cast iron grate for seasoning. It is Canola oil and I used it as the spray is quick/easy and less chance of missing spots with the oil coverage.
I don't have any type of heat diffuser in so I placed a turkey fryer thermometer in the top air vent. When it got to 550F, the CG thermometer read 370F. I put a second turkey fryer thermometer in and it measured the same as the first turkey fryer thermometer (within 5F).
BTW, I sealed the inlet air vent with the blue, ATV gasket maker and let it cure for 36 hours before I started the burn-in this morning.
OK Joe Vertical Smoker, UDS, Komado Acorn, Weber Kettle Ranch, Weber Kettle, Stok Kettle