Hi!
I've got a video series on Youtube on making scenery using extruded foam.
If you are interested you can check it out here: www.youtube.com/thebige61
E
There's 3/4 inch plywood under the track (which is probably a bit overkill for N Scale). The fumes on the cutter are minimal but then again I did not use it that much. I wasn't really a "high end" cutter....
Check these pages out to give you and Idea of how I did the framework, Roadbed, and initial laying of the foam blocks.
http://modelrr.oakviewresources.com/progress3.htm
http://modelrr.oakviewresources.com/progress10.htm
Hope this helps!