Measure the inside of the large cabinet. Take measurements of the sides, the back, and the top and the bottom of the cabinet. Measure the door, but subtract 1/4-inch from each of the measurements.
Obtain 1/4-inch thick cedar boards in the cabinet measurements. Your local home improvement store will cut the boards in the desired sizes.
Install the cedar boards inside the cabinet and to the door with the electric drill and screws. Make sure the edges are secure and tight next to each other.
Add 1/4-inch wide weather stripping around the perimeter of the cedar-covered cabinet door. You can find inexpensive weather stripping at home improvement stores. Use self-adhesive weather stripping for easy installation.
Mount small wire shelves inside the cabinet. Wire shelves for bathroom closets or kitchen pantries work well and come with the hardware for installation.
Set a tabletop humidifier inside the cabinet. Cigars need the humidity for freshness. Choose one that holds up to 1.2 gallons of water and will humidify for up to 60 hours before you need to refill the water.