Ceramic heat lamps are notorious for drying out the air. So to combat this, you can put an extra large water bowl under the lamp.

Cypress mulch is also great at holding moisture. Also a moist hide in addition to the regular hides will give the snake humid options. Basically just put damp (not dripping wet) spaghnum moss in a lidded Tupperware and cut an entrance hole making sure to file the sharp edges.