Question #1 should always be...are you using a UTH and if so, do you have it hooked up to a thermostat?
Beyond that, yes, blacken out the sides and back in some fashion. That makes them feel more secure in their surroundings.
A nice thermometer is the Acurite w/ probe that you can get from Walmart for about $12.00. The probe is perfect for hot spot temp while the body keeps check on your ambient temp and humidity.
A great way to maintain humidity is to cover the top with tape covered foil, leaving about 20% uncovered for air flow. Also you can change substrate to reptibark or Eco earth <or a mixture of both>, those tend to hold it longer under dryer conditions. You can also use plexiglass, drilling holes and cutting out a spot for a heat lamp if necessary.
At 4 months, your little guy is still a baby and will be overwhelmed by wide open spaces so clutter is good. Some use crumpled paper, others use vines and leaves to fill in that space.
Hope this helps...