I use oscillating fans to circulate air on the tubs and add or fill in holes as needed to maintain humidity levels. I'm using individual tubs but I imagine the principle would be the same for a rack...
As far as the gages, I just basically velcro'd the Accu-rites to the inside of the tub. There is a DIY stickie that shows how to modify AccuRites, if that is what you are using, so that all of the sensors are in the enclosure while keeping the unit outside. I'll see if I can find it...