Weber porcelain coated cast iron grill grates.

So I picked up a genesis 300 series and it came with the stainless steel grates. I'm thinking about getting a set of the cast iron and just putting one of them in, so half of my grill will be the cast iron one, and the other side will be the stainless steel. I would probably put the cast iron one over the side with the high heat sear burner and then the stainless steel over the other side. I had a cast iron grill grate before on some other kind of grill, and I remember being frustrated with how much it rusted. I'm not sure if it was porcelain coated, though. Anyone have any experience with the weber porcelain coated cast iron grates?? It's about $70 for a set of em, so I don't just wanna go spend the money to find out they are gonna rust out on me. I can do maintenance, but my grill still has to be out in the elements. I do have a weber cover for it that I use religiously, but you can't help a sudden downpour from time to time.

Thanks!