2014 136” HR
Attaching the floor should be necessary only to hold it in place, not to keep it flat. If it does not lie flat on its own, you need better plywood. Depending on your location, you may need to visit a real lumberyard. I haven’t seen anything decent in a box store in several years. It doesn’t have to be fancy—my 1/2” exterior ply was flat as a flitter.