Home alone tonight and rubbish TV, so the engine house has moved on quite a bit. Walls clad with lapped planks, internal floor done and dirty - can't really tell what it is, after all my worrying. In fact it's planks along the rear wall that can be seen through the door, and plain card (concrete or just filth) between the rails and on the nearside, which is all but invisible. Had some fun adding detail parts - gas cylinders, a compressor, cans and a jack, and made two tool cabinets out of a cardboard outer box from a glue tube.
Should be able to do a little more tomorrow, and so perhaps pictures by tomorrow evening.