jwhitten:However, I mostly agree with the other respondents that unless you have some special need for a suspended configuration, you'd probably have a better bet with just building up the benchwork from the floor.
Yes, after consideration of all the ideas, I think that's the way to go. I was thinking I'd save myself some lumber and construction, but all I will save is about 20 linear feet of 2x3, and it will probably be simpler to just build the legs than to work out some elegant way to mount it on the wall.
Since it's 19 feet long, I'll be building it in 3 separate sections. It's not meant to be truly "modular," since there are far too many tracks crossing the section boundaries, but it would allow for a one-time separation if it had to be relocated at some point.
Thanks for all the help and suggestions. Time to buy lumber in a few weeks, so I can have the benchwork upstairs in the warm train room by the time winter sets in.