[Just catching up on posts after a move and computer / ISP switch]
About 10 days ago, there was a discussion regarding spline construction. By
coincidence, there is an article in the latest Railroad Model Craftsman (Plastic Air Cell
Layout Construction, p. 70) which may be of interest. It is especially interesting
because a) the materials are very lightweight and the finished project appears to be
surprisingly rigid and b) the author provides some in depth info on the properties of
the materials and the adhesives needed.
The road bed rides on a series of foam splines which can be easily made using
common handtools and adhesives. Being mounted on a type of foam-core, it is much
easy construction than the wood spline layout bases I have seen. The combination of
technique and materials may have something going for it.
I think the article could have been better written (or a better editing job) for
comprehension, but it is a technique I haven't seen before, and it could be VERY
appropriate for portable Z layouts. (Although the cost is an important factor.)