As for humidity you could mist your cage daily, or use some aluminum foil or plastic wrap on top of the mesh to help hold in humidity. You could also put your snake in a tub. I keep all of mine in sterelite tubs. I use the plastic wrap on my poison dart frog tank. You could also use a larger water dish in combination with covering the screen top. You can also use a bark substrate like cypress mulch (make sure it has no chemicals in it though) or maybe even repti bark although I think cypress mulch would be cheaper. Mist it once in a while and it should help keep your humidity up. Like I said though, I use sterelite tubs and have no issues with humidity. I'm sure others will chime in with more ideas though.
If you're having a really hard time with humidity you could also give him a humid hide. I used to do that with a ball python a few years back. I used an appropriately sized closed container (I used a country crock large container) and cut a hole in the top large enough for my snake to get into. Inside the container I used moist sphagnum moss that I bought at my local pet store. I moistened the moss to the same wetness as a well wrung out wash clothe.
Hope that helps.