Hi Ed,
Sorry I didn't get back to you personally regarding your question. Got caught in the Forum transition.
If you'll look on the Construction page, Phase 7, I show how I use ripped 2x4 strips for the initial spline layout of the roadbed. To that I glue Homasote ripped to 1.5" to match the spline. Then three more strips of Homasote followed by a final wood spline. I use deck screws as temporary clamps, working rear to front. The yellow carpenter's glue dries very fast. I belt sand the top as needed to square everything up. VERY stout spline roadbed when done plus the natural easement in and out of curves that wood splines provide.
As Bob said, the Micore is great for yards, etc. But I use Homasote for the spline roadbed as the Micore tends to snap when bent, unlike the Homasote.
Hope this helps,
David