Well, if lightweight didn't work, then I was going to go the opposite route and make it heavy-weight. I cut two sheets of 3/4"-thick MDF and glued them together to form this 1-1/2"-thick board. After painting it, it was ready for track, right away.
Since MDF doesn't transmit sound as much, I had skipped the cork layer and went straight for laying the ties for this five-track yard at the coal tipple.
The one thing that was a success from the previous experiment, was the method of laying track. So, I did these the same way. I have a detailed article about that here.
After all five of the tracks were done, I put blue masking tape around the edges of this small module and covered it all with coal-based ballast and lots of diluted glue. While this looked exactly like the picture I had in my head, it turned out that too much of the ballast was too close to the rail. The cars wouldn't track on it very well, and trying to clean this out was an effort I started but, in the end, it proved too much. Nonetheless, I liked it, so I kept it around for while.
Not quite ready to give up on it yet, I built this framework out of 3/8" MDF. The legs screw into the wooden blocks in the corners, similar in concept to the common foamboard experiment. I figured this was better since MDF is supposed to be stronger. While MDF is heavy, using the thinner version of it should mitigate that somewhat.
The design concept behind this experiment was similar to my current layout (Layout #7), in that the bottom of the module would be closed, but the top, the scenery layer, would be able to be opened when work needed to be done. So, this photo shows the right-side-up view of the module's internals. The crossbracing was necessary to strengthen the sides, and the holes were drilled to remove as much material as possible without loosing structural integrity, and allowing wires to be routed through them.
This is what the bottom of the module looked like, with the legs hardware visible in the corner. The whole thing was painted at this stage.
The coal tipple yard track module was glued to the module frame, and here I am installing the cardboard strips to form the foundation for the scenery layer.
After applying plastercloth and Sculptamold to the scenery layer and subsequently painting that, this is where the module stands now.