nice setup, i love rubbermaid grows, im currently finishing up my first hydro rubbermaid grow, and the one thing i suggest is put a screen in there and train the crap out of your ladies to conserve space. as for humidity, you could obviously use a humidifier, a bottle of water probably wont work that well, it needs more surface area exposed to evaporate, in mushroom cultivation you soak perlite in water and then put it in a container to raise humidity and it works great. maybe also a flat pan of water positioned so the air from your fan hits it.
also whlle theyre young throw a humidity dome on them, super simple all you need is a piece of plastic