I've been getting on with things. In order to 'bridge' a large gap associated with a window located in the wall on which the shelf layout is attached, I opted to use some high density insulation foam. Its stiff but light - I can see why many use it for exhibition layouts. Apart from applying some more cork for the track bed, I've also been 'sculpting' the foam. It's planned to construct a low trestle over a 'swampy, wet topographic low'. Its still a work in progress...
In response to Phillip Overton's question in my last post (sorry Phillip, I only saw your comment the other day), the brackets are removable. I built the layout such that I can save the metal brackets and wooden frames, along with (of course) the layout modules. Thus, I can take it with me in the event that we have to move house etc. So I guess its 'semi-permanent' in a 'semi-removable' kind of way!