Mine's still a work-in-progress but I used a smooth door for the layout base and have it resting on a portable but sturdy table...the type you can find as some of the buying clubs. It has a particle board top, laminated surface, and a metal frame all around with swing out legs that can adjust to various heights. That way, I can have it placed to about 48" or so for me and drop it to 14" for the kids if I want. I'm working on a way to attach the layout to the table - maybe using industrial velcro to allow the two surfaces to separate if needed. Also, I need to attach the power pack to the table, which I'll probably mount beneath the table surface in a custom-created drawer - much like a computer keyboard drawer. You can get drawer glides at any home store and build a drawer to fit your needs.
Sorry, that was long winded...the short version is the collaspable table gives me portability and various working heights. The only thing I make sure of is that the table surface is level when on the carpet.