I bought FRPP ones from Summit, I think. My buddy bought them from me. He had them on his for a while. They never even begin to rust. I'll ask him how long cause I have no idea!
i couldn't tell you what brand i have as they came on the car when i bought it. the plates rusted really bad but the rest of the kit is fine. i had a guy make me new ones out of stainless 1/8" plate.