My wife and I are in the process of revamping our basement and are hoping to install a new floating mantel over our gas fireplace in the basement. I'm hoping to get a piece of 2" thick, live-edge cedar for the mantel. My question is how best to mount it to the drywall above the fireplace. My concern is that our basement is framed in with steel studs and I'm concerned about the weight distribution of the wood slab. The mantel would be approximately 70" wide, however, I have access to a crawl space behind the fireplace and found that in addition to the drywall, a sheet of 19/32 plywood has been installed behind the drywall for presumably, extra support.
With that, what would be the best way to mount this? I've done a bit of searching online and haven't landed on anything. I've read anything from toggle bolts to lag bolts to carriage bolts with nuts and washers. Should I aim to go into the studs or just utilize the plywood backer or something completely different? Any thoughts or tips would be very appreciated!