Interior backdrops

Your best bet is to do a Google search for a factory interior, print on paper and insert it into your structure.

Rich,

Like PRRHORSESHOECURVE said, use Google search for images.  Try searching for things like "factory interior" or "vintage factory".  I've had good success searching for the things the factory or building produces, like a hardware store sells paint.  I searched for "shelves of paint" and clicked on the "images" button.  I copy any picture I like to a folder.  I don't use any fancy software; my go to is Microsoft PowerPoint.  I drop the images into PowerPoint and draw my interiors using the simple shapes, colors and images.  Biggest tip; the natural difficulty seeing the interior through scale windows and doors means your interior pictures don't have to be supper detailed or dead accurate.  You are actually just "suggesting" detail, and the viewer's mind will run with it.  you can crop, cut, and paste images in PowerPoint pretty easily.  When I'm done, I "group" all the pieces of my interior and save as a JPEG file.  I than insert these files into a blank Word document, and scale them using the image size button.  The measurements don't need to be precise, I generally round to the nearest scale foot using decimals, i.e., 1 O scale foot equals .25 inches.  I print my word documents at 100% on photo paper using my desk jet printer.  I cut the images out and glue them to the interior walls with spray glue.