One grouping tool step to add -- inverting the normals, because you'll be looking at the inside of these props. RDNA have some good scenery props. Their Skydome is a freebie, and there's also a lot of free textures, both the sky and tileable ground textures intended for their Microcosm product. Many of the scenery propsets I've seen have a slightly raised rim on the ground, so you don't see the transition between ground and "wall". Consider having two or three concentric wall props, each using a transmapped skyline. The outer ones would have increasing amounts of blur applied to their texture and transmap, and the texture greyed out, to emulate the effects of atmospheric haze. With Poser 5/6 there are various Material Room methods to replace those small textures with shader nodes. You don't want the scenery walls or skydone to cast shadows. In P5/6 it also makes a difference to apply textures to the Ambient channel rather than Diffuse. That way, you don't see shadows cast on the background at render time.