Danny, I put my grommets in the holes where the bracket bolts through the side, at the upper and lower grate locations. I just drilled out the sidewall and the bracket to the desired size. Some hi-temp black BBQ paint to touch up the areas around the enlarged hole will keep down any rusting.
Some folks just go through the sidewall at those heights, leaving the brackets be. Just your preference. If you do it that way, be sure to use some painters tape to help prevent chipping, and try and use a step drill if possible.
I went through the existing holes too. Initially I did not like the idea of making more holes but after doing some other mods and cutting holes for vents, as long as you are careful and use tape to start you should be fine. Others have but I would not recommend a punch to start a new hole.
Grease from the cooks will take care of anything on the inside and a bit of paint outside if you need it, you should be
fine.
