I’ve been making progress with the generic terrain boards; there are 4 though only 3 are in these photos (CDA):

These use 600mm x 1200mm x 50mm thick grey rigid foam, by Panel Systems. I bought a carton of 6 so I have 2 spare for ‘special projects’, whenever and whatever they might be.
My boards will be flat rather than contoured, so largish terrain items can sit level when placed on them; thus there won’t be any elevations (such as fixed hills) but there can be depressions (such as a fixed river).
The 4 panels, three with roads/tracks and a fourth with a river crossing plus a ford or watering place, were marked out, then the recesses cut out.

A gauge was used to arrive at a fairly level river surface (note river surface, not river bed):

The bridge sits on recessed pedestals, with the bridge being removable for storage or to be blown:

The river bed was plastered and sanded, albeit not completely smooth as I want some rise and fall to suggest movement:

The basics of the bridge pedestals:

And with green stuff added:

And the bridge test fitted:

With sieved Sharp Sand glued in place to create ground cover:

With Kiln Dried Sand glued on to the tracks and river bank, the tracks being brought up to the level of the ground cover and scored for track and transit marks:

The bridge bedded-into the terrain:

A couple of views of my hamlet in situ, showing how it’s tracks overlay the boards’ tracks:

