I have about three projects on the go at the moment, but keep trying to focus on Rhiw.
Time for the retaining wall at the rear. When you start looking for photos of what you think is a very common railway aspect you find that it isn't. Softer embankments are a lot cheaper I suppose. What you do notice is that walls are at least partly sloping often with a more vertical upper part so this I the direction that I've gone in.
Materials thus far are a lever-arch file... well a defunct file with the metal ripped off and the plastic coating removed leaving me a couple of large bits of 3mm thick card.
Scraps of corregated box for the formers.