garwig, I coated mine with shortening before I used it for the first time, but it probably wasn't necessary. I always store it inside the Egg to keep it from getting wet and it's been fine. I use one mostly for cooking steaks, with the "point" side up. With the "flat" side up it is useful for things that might have a tendency to fall through the grill, because it has more surface area than the regular grids.
There are post on the forum every otherday about cast iron grids. Try doing a search and I'm sure you't find the information you need, o just look back over the last 30 or so topics and you find post about grids
garwig,my cast iron is what I use all the time. I had Charbroil grills for the past 40+ years and that is what they had so when I got our large BGE I boought the cast iron. I did not season it and it stays in the BGE all the time with no problem as far as rust etc. We live in Sarasota, Florida so if it works here on the Gulf of Mexico it should be good any where.