Haha! I just emailed your hubby and you some ideas. 
You could do a set of bars fairly simply by drilling holes into two 2x4's and inserting broomsticks. spray paint the whole thing black. If you back light it, it would cast an impressive shadow against a side wall.
Part of creating an environment is using all 5 senses. Set design and costumes will give you visual, but what are you doing for touch, taste, sound and smell?
For sound - make a background track that has "prison" sounds. buzzers, clanking metal doors, guards voices, etc
No idea for taste and touch, but for smell I'd tell everyone not to shower for a few days so they smell like sweaty prisoners. 
Commenting by HaloScan
