There is a very large layout in Allentown modeltrainexhibit.com
that was constructed using steel studs and 3/4 plywood on the top. They used heavy gage steel like one would use to construct a building. I used steel studs on my benchwork for support on one side with no issues. I framed my basement walls with steel studs and built a boxbeam out of the stud material and fastened it to the outside walls and attahed the top of the bench to it. The rest of the bench is made from 1 X 3 plywood strips that i bought precut. They were 16' X 2-1/2" X 3/4" Everything was covered with 3/4" plywood and a minimum of 1" extruded foam board. I use Fastrack and have no noise issues.
