Orient Express
My current project is built on two closet doors. The hollow doors let me install the stair wells and freight elevators for the station platforms.
My Williamson W.Va. project was built on 1/2 plywood topped by homosote. I drew a 4" grid on the plywood and with a door-knob hole saw, cut circular holes.
This lightened the sections, considerably. After glueing on the homosote, I attached adjustable folding table legs to the underside.
I used a cone shaped router bit to cut the ditches along side all the track. (Be sure to do this outside, as a great deal of homosote dust is created).