stream feature
I'm assuming that with the stream feature I'll be needing 2" of foam on top of the plywood.
Well, that's one way to do it, probably the most straightforward (and the most in vogue right now in MR). I'm sure others can chime in as to their favorite methods.
My first thought was this; I'd say if you were going to go cookie cutter with the lower roadbed then the stream bottom would just be the lowest level on top of the benchwork. But looking back at the plan there's so much area that will work naturally on a tabletop with only minor depressions for roadbed shoulders, culverts, pipes, etc.
SO, how 'bout a layer of 2" under the whole area with the creek cut out, with a sheet of homasote used cookie cutter fashion under the track and sheets of 3/4" beaded foam beneath major trackside structures. This gives a nice elevation for track to be above scenic features like roads & streets, other non-railroad structures, etc. so you don't have to go gouging out large areas of foam.
When I was living in OH I remember finding packs of the beaded white foam in sheets about 1' wide and 3 or 4' long, made for craft projects in Home Depot. Didn't look for homasote but I do remember seeing the big sheets of pink foam.
(Don't be deterred by what others say about the white foam. Use a fine tooth serrated knife or sharp paring knife and quick, short sawing motions to cut it. Beading will be minimal. And you
don't have to paint homasote to seal it, either. Check out the homasote website for proof. However, it is a good idea to paint it gray just until you balast, to give the illusion of balast. Just draw your center line once the paint has dried and go from there.)
Looking forward to more pictures.
Galen