We went down the path of a hollow-core door, 2" pink foam and then woodland scenics risers/inclines (with plaster cloth… here we decided the stuff from Amaco (sp?) was easier to work than the woodland scenics stuff.
Makes for a reasonable-sized n-scale layout and it’s still very light.
I built a 4 sectional 8x12 HO bench work with 1/2 inch plywood base topped with 3 Inches of extruded blue foam. Since I did a lot of cut outs in the plywood and had 1X4 stringers under neath, the 4 sectiions came out very light weight. I can disassemble and move and set the whole thing up by myself with no help. All four sections bolt together. I couldn’t be happier with the results. I went with the 3 inch foam (Expensive) because I wanted to cut deeper areas and rivers. and most important, the layout is strong enought to stand on. I have already don’t this for a few hard to reach area. I just put down a 2 or 3 foot oiece of plywood on top of the foam to stand or kneel on so it dosen’t dig intom the foam. Works great.
Hope this helps. The layout is also free standing. I have posted some pics in the last free weeks if you want to check it out.
DON