I was concerned from the start on the durability of the Elmer's foam board when exposed to wet scenery or even spraying a latex paint coat. This is why I have it covered in 1/6 plastic. I next plan to remove the plastic and paint it with a flat latex sand color to form the earth colored underlay for the Port Costa yard. When that step has been completed I can begin to lay track. Port Costa is only 18 miles away from my home and I been there many times.
Track will not be laid directly on the foamboard/plastic surface. I am using Woodland Scenics dense foam roadbed underlay for all trackage. I have used this in the past on a previous layout with good results. Ballasting track is a long way into the future but the layers should provide protection to the foam board layer.
This layout is being built before the advent of true dead rail so there will be some wiring. Much of it will be "trenched " on the surface in true prototype utility fashion rather than under the table. I detest under the table wiring with great passion. I currently use DCC to eliminate the necessity of any block style control. If I could eliminate the need for electrical power flowing through the trackage I would.
I will be cutting into the foam board layer to build a turntable pit. The pit needs to be 20 mm or 3/4 inch deep. The benchwork has been designed with that in mind.
I checked on Gator Board and Gator Foam board availability. I could not find retail sources that would sell it in large enough sheets in small quantities without special ordering. In hindsight I probably could have gotten away with 1/2 inch plywood much cheaper than the route I have taken but it is in my nature to take the less trodden path or try to find a new way.
Current as of 8/25/2019. More turnouts have been ordered to replace Peco Code 75 stand-ins.