Go with stainless. Many high end grills come with 3/8" round barstock. My Komodo Kamado comes with 3/8" upper grate. As you can see, the 3/8" rods are only supported around the circumference of the 23" grate. Depending on the dimensions of your grate, you may not need additional supporting rods running down the center of your grate. That will make for easier cleanup, and I can't overstate the importance of easy cleanup.
You should be aware of grill scrapers made for oversized bar stock. The Billy Bar
and the Grill Floss
are two that will work very well. You must ask Billy Bar to make you an oversized unit for 3/8" because their standard one is for 1/4" stock. They'll do it, though.