Although wood is most commonly used to frame layouts, there are other materials that can give excellent results. One approach used by the late Mr. Walter Hunken of Atlanta particularly appealed to me. Rather than using wood, he chose a material called Foam-core®. This material is soft foam plastic which is laminated with a harder paper sheet on each side. It is easy to cut, requiring only a knife and a straightedge. It is cut much in the same manner as sheet rock, by cutting one face of the material with a sharp knife, bending it back upon itself and then cutting the remaining material face.
Mr. Hunken also cut risers for the track out of the foam core, and attached them by using hot melt glue. Since his layout is small, the foam core did not need to be reinforced. If you choose to do so, you could cut strips that would strengthen the layout the same way that the 1 x 3 does.
In any case, the net effect is a layout that is easy to construct, is lightweight, and uses inexpensive materials. In keeping with the lightweight approach, the two-part expanded foam scenery approach is a natural one.