Updated 7/20/2019:
Today I installed the plywood flooring supports for the styrofoam track side embankments. The original intent was to use 1/4" masonite, but it seemed too flimsy. I ended up doubling the number of vertical supports & cross-beams for this, thinking that would be enough for the masonite. Ultimately, I decided that wouldn't work and used plywood. If worse comes to worse, I can stand on it. Let's hope that never becomes necessary.
Here's a 3/4s view from over head of the rear-most flooring.
This is a view from straight on (front to rear).
In this photo you can see the flooring edge-wise.
Here's another edge-wise view of the end of the flooring. I took this by reaching the camera through the Stone Arch.
Finally, here's a shot of the front flooring in place. Note that the cross-arms extend out from the rear wall to the depth of the layout (and fascia).
More when I know it. 
George
