Usually I found them in broken boxes that has degraded a bit, though some species (like Latiblattella rehni) seem to like intact boxes more than soggy degraded boxes.
I've not been posting pics much here lately bc whenever I post new pics on my FB the links for my old pics no longer work so I have to update the posts on here to make the pics visible again.
P. fuliginosa naturally occurs at my place and occasionally comes in from outdoors. I used to raise large number of beetles so I had a box full of substrates and rotten woods, and those darn Periplanetas were feeding off of those and breeding in there They also got into my Blaberus containers and started breeding. It took about a year to get rid of them from my house but now I have Supella longipalpa breeding here