That's a nice looking setup you have there. I've only ever used certain types of cocoa bedding and never really had an issue with humidity except for maybe low 50s in the winter where I had to spray a little bit. Every other time, it's sitting around the 60-70 mark. I didn't see a water bowl in your enclosure (which I'm sure you have) but you might want to get something larger to help w/ humidity.

As for the temp gradient, did you consult w/ the Bob at Pro Products on the wattage needed? Your gradient doesn't sound too terrible but a couple more degrees on the cool side would be perfect.