Good things come in narrow packages

[doctorwayne]

Unless you can restrict the viewing angle, backdrops with any hint of perspective don't usually work very well. I think Pete's suggestion of a plain sky with perhaps some muted colours along the horizon would work best, especially when you're running trains. However, you could also experiment with temporary backdrops that could be inserted into the scene for photography. These could be painted, photographic or very low-relief items. The latter could be free-standing "structures" that would lean against the existing backdrop, while the others, mounted on heavy cardstock, foamcore or styrene, could be in whatever perspective you wish, as you could set up the camera at a point which would make the scene look best. If you were so inclined, you could even have multiple backdrops of different types for the same layout area, to be used from different camera angles. Photographs of the same scene taken from different perspectives would work, or totally different scenes for a variety of effects. These would work as either a complete background scene, with its own sky filling the viewfinder, or cut-outs, with the layout's sky showing behind the temporary scene setting.

Wayne