Not sure of the size i need since I haven't bought the pot. I want to use stainless stell as aluminum deteriorates into the food when salt is added. I have a turkey fryer, but I don't want to use it or an aluminum grate for this reason. The trivet idea sonds decent. I have seen some stainless steal pie racks. Rocks could work as well. And, yes I have just thrown them all in and let the ones at the bottom "soak."
I have one pot I got after my father in law passed away. It's aluminum, one of his buddy's made him a grate out of aluminum. He used it about 20 years before I got it and I used it several years before I got my first stainless pot. I still use the grate in a small stainless pot I use when steaming a dozen or so. The aluminum is rough but it's still doing the job. I rinse and brush it off after every use. It does flake a little if not used for a long period of time. I just rinse out flakes before use. No difference in taste of crabs when cooked in all stainless pot with stainless grate, or aluminum grate or aluminum pot. no aluminum taste or anything like that.