I started with several frames or tunnel x-sections cut out of thin MDF. These were spaced about 15 cm apart and joined up with cardboard strips glued to the MDF frames. You need to cut the cardboard a bit longer than the gap to be covered so that you can push it up/down to create terrain variation.
This was covered with modroc / plaster of paris bandage, taking care to have plenty of overlap. Also smooth the plaster when wet so that it creams up and covers all the holes in the bandage.
A base coat of dirty green was then applied. Rocks were undercoated in black.
The green bits were coated in diluted PVA and covered in a mix of half a dozen scatters. I did not pre-mix these, but simply sprinkled on various sorts until it looked right. I've predominantly used three types: (a) Woodland Scenics Fine Turf Earth Blend, (b) Woodland Scenics Small Foliage Green and Olive (c) Small quantities of mixed green, purple and a tiny bit of grey old-fashioned woody scatter. I guess the thing is to make sure it does not look too green - natural landscape never does.
The rocks were drybrushed in increasingly paler shades of grey, until almost white. You probably know the technique - load the brush, wipe it all off again and paint with an almost dry brush. As you go paler, you focus more on the sticky-out bits and make sure not to recoat the whole lot again.
Didn't do much scenery of late - but did take the paintbrushes to my new secondhand gronk last night:
Supid question about 08 class shunters - which end do you call the 'front'??