I have kept both atrox and cerastes. What many people don't realize is that in the middle of the day, C. cerastes DOES indeed take refuge in rodent burrows, holes, etc. Especially here in Az in the summer time you will not find them out and about, except at night and in the early morning. The humidity underground is quite a bit higher than at the surface.
While they are certainly an "arid" species, I have found that misting them down occasionally (as well as their hidespots) works well. The remainder of their water they get from their food. However, I have NOT had success in keeping C. cerastes in a completely xeric environment. I also find that PVC pipe works well as their "burrow". These are just tips that have worked for me with C. cerastes, so hopefully they might prove helpful to others when working with this interesting little snake.
As far as atrox, as long as the enclosure has adequate ventilation, I have had no adverse effects when they are kept with a water bowl in their enclosure at all times. Basically, I've had success when I've kept them in a warm cage, a hidespot, a water bowl and a healthy supply of rodents.
I would consider C. cerastes a "specialty" species and C. atrox a "generalist" species. All things considered, I've found C. atrox a much easier captive in terms of husbandry requirements.
-Rally 'round tha family,
-AzAtrox