The photos below show how the track was laid. I am using Atlas code 100 track on this micro. I used wood glue since it is resistant to water/alcohol after it has dried. It has a fairly strong bond but is not too hard to pry up if you accidently glue a piece of track that is not supposed to be glued down. A nice feature of foam core board is you can use push pins to hold everything down while the glue dries. I was careful not to get any glue under the removable track sections. After the glue had dried, I glued individual plastic railroad ties under the rail sections where gaps were present. Everything is staying put, even with extreme humidity changes.
Up next in Part 4: Wiring the layout.