Thank you for all the nice comments. It's the people on here that have inspired me to create this and also described most of the techniques used. I feel slightly guilty about not having "in progress" photos but I only ever seem to think about it after the event.
To answer some of the queries raised:
This was taken after I had removed the DAS I had put down to give a filled in track effect then I decided I didn't like it!
Both locos are on Smokey Joes with a bit of extra weight added. They were both second hand and the green loco is a smoother runner than the red one.
Some more photos:
This one (above) was taken before most of the undergrowth (hanging basket liner) was put down. The log pile at the front hides switches for two isolating sections.