JohnJr,
Thank you for the suggestion. Yes, I can see how the plaster cloth would give something rigid to support the track. Your comment addresses the issue that I am facing since I made the decision to use foam to make my grades instead of wood.
My original plan was to put down a base of wood then put simple 2x4 risers on top of that for the grades and level upper track. I would then use a wood-Homasote-cork sandwich for the roadbed whether on level or a grade. I happily went on with that on the level area then felt overwhelmed at making the transitions from level to the grade. That is when I decided to use foam. That was fine until I realized I didn't have a good transition from the existing risers to the foam.
This photograph shows two mismatches. On the left, you see the top of the 4% grade which comes up to the top of the risers. When I shimmed up the Woodland Scenics grade with 1" blue foam, I forgot that the risers were cut to have 5/8" of plywood or MDF/OSB before putting down Homasote on top. That's the first mismatch.
On the right, you see the risers shimmed from 5" to 5 3/8" to give more room for trains to pass under my one overpass. Carrying that through, I would still need to shim the middle section of risers to 5 3/8". That means I need to raise the grade even further.
Here is where I temporarily placed sections of plywood down to make sure all my shimmed risers are level and at the same height. I will need to work from that overall height around to the grade I showed above.
So in effect, I have been spending some time spinning my wheels on this, but all is not lost. One thing is certain. Everything is nice and solid so far! 
I have been thinking of adding more blue foam under or on top of the Woodland Scenics foam to make up the difference in height. Other suggestions are welcome.
Have a great week and stay safe and healthy!!
