Again, I hate to beat this like a dead horse, but just make sure to feel the inside of the bin prior to purchase. I believe I had issues with a heavy duty "rugged" type of rubbermaid and baby nymphs climbing up the very fine texture. I'd hate to see you spend money on a bin and roaches then discover that you need a new one and have to transfer them ; ) Just make sure it is nice and smooth...generally if it is super sleek on the outside it will be a good indicator that the plastic with be nice and smooth on the inside. The texture I am talking about is almost un-tangible but it is enough for the newborn nymphs.

As for humidity: the microenvironment within the bin will be unique and can easily be adjusted. Too humid and you will note condensation, hypo-pigmentation of nymphs, and potentially mold growth. Too dry and you will have serious molting issues. Adjusting the size of the ventilation and keeping a supply of water crystals in the bin will generally keep things nice and comfortable for them. I wouldn't sweat it too much, roaches are much hardier than crickets and other feeders - but if you notice problems with molting or other indicators just mentioned, you can take counter-measures to ensure they bounce back...too humid and you can increase ventilation, too dry and you can decrease some ventilation and/or you can add a container of water in there inaccessible to raise ambient humidity (or keep more water crystals in there for moisture source). I've honestly never measured the humidity in any of my bins and it can certainly vary, but I'd wager roughly 50-65% is ideal.