The tubs, only if there is a shed cycle going on. Aside from that, they hold enough humidity.
My display cage I mist about once the week and that works great. I use one of those gallon/sprayer with the pump. Makes life so much easier.
How much you have to mist probably depends on the humidity in your house. If you have low humidity you will have to mist more often. However, with the right mist bottle, that isn't even an issue, imho.