What to use is really entirely up to you. There is no "best" method. I am working on a small 2' x 4' portable layout, so I went with a foam base. I used 1" blue insulation panels I picked up at Lowe's. The same can be purchased at Home Depot. I then covered it with some Scultamold to smooth it out a little more. Don't be fooled by the toxicity of these materials. Remember, they are being used in home construction and MUST meet certain guidelines. They are no more toxic than burning wood, vinyl siding or anything else used in building a new home. Saying that, I did all of my hot-wire carving in the garage to save myself from the spousal rants. The foam is very forgiving, and lightweight. Crumpled newspaper and hydrocol is harder, still lightweight, but makes a different kind of mess than the foam. It's all up to you. That's what makes it so much fun. Experiment on something small. Get some blue foam, stack it up, in a 1' x 1' square, try carving it. Have fun! Greg
After a couple of articles and posts on lists, I have to say I'm leaning towards 1" aluminum (aluminium locally) angles and a foam base for my upper level. My lower level is a mix of old plywood, masonite, and one unidentifiable cardboard type section, mostly covered with sheet homasoate, and cork strip for roadbed where the track would be seen. Over L-girders of course. Some of these materials are over 30 years old (they were the base for my first N-Scale layout in the 1970's) and it's a shame that most of those trains aren't still around... Most of the upper level will be industrial or yard trackage so more down in he mud. If I can find the right foam, I'll give it a whirl...
Here's a 3' x 5.5' frame (hmmm, don't know why pic is not direct linking, you'll have click on the link): Here's the same frame stained and 1.5" pink foam added: Now comes the wiring underneath: Here's an in progress shot:
