Cover the screen top completely leaving just an opening big enough for the bulb. This will hold in more heat and humidity.
Lose the bark. It's too dry and it will mold very fast if you try to mist it down for humidity.
The best substrates are newspaper, paper towels, cypress mulch, or Aspen.
Aspen will also mold quickly if misted for humidity but if kept clean and changed this should not be a problem.
*edit*
You can use foil taped down to cover the screen top. You can also get a thin sheet of pink insulation, paint it whatever color you'd like, cut it to fit the sides and back of the tank, and put it on the outside of the tank. This is decorative, will help keep the snake calm as it cuts out reflection and glare, and it adds a lot of extra insulation![]()
You can get creative!
Make sure you have at least one (preferably two) tight fitting hide boxes for the BP.