Why have a soundstage, when you can have a space with easy access to the outdoors as well? Over the years, my garage (without cars in it) has become a multipurpose filming location. The existing lighting is even, and can be enhanced by opening the garage doors and letting in natural lighting. If all the junk is cleared out, you have your choice of blank walls. If the scene requires a more industrialized setting, the metal doors themselves can be the background.
For the interior of a prison camp, a combination of these backgrounds was perfect. Blank walls puts the focus on the performers while closed garage doors show the possibility of escape. Of the scenes filmed here, I ended up cutting most of them, but it was an enjoyable experience for all of us involved.