I wanted to add my experience with the grommets.
I picked up the lamp hardware to do both of mine. The WSM went without a hitch! Perfect holes and looks and works great.
My OTG on the other hand, it appeared the porcelain may have been a little thicker, maybe not, but when I removed the tape on both sides, a porcelain "shell" came with it. Same new bit, drill everything. One side took a bigger piece than the other, but both lost a chunk.
I'm not too worried about it, except the appearance, since it's not down into the metal, but I was really surprised. The WSM is nearly brand new but the OTG is a year or so and has cooks on it as well as has been through record cold temps for north Texas earlier this year and now record heat streak. I can't imagine that would have anything to do with it, but it just seemed more brittle, even with 2 layers of tape and a new titanium bit.
So it goes to show, it can happen no matter what precautions you take.
As an aside I was surprise how think the sheet metal is on these things. I was impressed.