The first experiment was to use 1/2"-thick insulation foamboard bought at the home center. This 4' x 3' x 3' monster was glued together with construction adhesive, and the joints taped to act as clamps. This first photo shows it upside-down.
This shows the underside of the bottom of the module. The back of it was to have a creek, so I cut the creek's profile into the surface.
In this photo I am gluing down 1/2" ceiling tile squares upon which the layout will be built. I have always been a fan of shadowbox-style layouts, and so the idea was that the left and right side panels would eventually have a disguised "tunnel" on each side for the track to come through. The rest of the box would keep the viewer's eye from wandering. I built this thing on my workbench in the garage. When it was time to bring it into the house and to the room where my layout resides, reality hit. Despite the fact that this unit didn't weigh much, it was a monster to move, and I was literally unable to get it through all of the doors. Ooops! So, this experiment was written off as a loss, with several lessons learned.