Many people will probably disagree with me, but I have had my snakes in a rack for a year now, and during the winter when we keep the heat at about 68 degrees, my tubs rarely go above 70 for an ambient temp. I keep the hot spot where the flexwatt is between 90 & 92. All of my snakes eat regularly and have never been sick with RI's or anything else. Like I said, many will probably disagree, but I haven't had any problems.

As far as humidity, you probably need to drill some holes in the side of the tub (about 1/4" or less). Start with a few, and then gradually add more holes until you get the humidity where you want it.

Good luck!