So Creazione blog has a tutorial for how to make a stone wall backdrop for 1:6ers without spray painting anything. This will be perfect for Lucian's castle! I just have to find a sheet of appropriately thick Styrofoam!

EDIT: Or I could just be really lazy and find some fabric with a print of a stone wall on it, which I did. I think I'll be lazy. It's cheaper than buying Styrofoam and paint, actually.