@argentflame the baby q just had light surface rust on it I really only had to brush it all over a couple of times then I rinsed the grate, dried it and seasoned the grate like you would a skillet in the oven. The baby q grate is small enough to fit in the oven with no problem but if the 320 is a one piece grate that may be a problem. You could always season on the grill though, I am sure it isn't necessary to use an oven I was doing what I have always done in the past with cast iron.
On the 200 the rust was more severe and a couple of the grates and the under side lost a bit of surface area to the rust. I brushed them really well and soaked overnight in vinegar then brushed again before I seasoned them. I imagine with the high heat of the burner I will be seasoning them more on the grill but that isn't a problem.