The Suburban has sheetmetal crossmembers under the plywood as well as two sheetmetal cross braces that connect to the crossmembers. The crossmembers have the triangular attachment. These crossmembers are mounted to the plywood itself. The seat mounting is terrifying. Before converting my wife's Suburban to a steel floor I was going to install more crossmembers underneath to attach the keyhole plates. If anyone needs photos of these crossmembers and cross braces I have a set of loose ones.
