If you really want to mount the hygrometer in the front face of the plastic or in the lid you will need a drill and a large bit or cutting tool to fit the diameter of your hygrometer. Many are 1″ wide.
Open the KRUS and carefully remove all of the stickers
Clean all of the parts with soap, you don’t want anything making your smokes smell like plastic or getting dusty
Insert the included dividers to help stack your stogies. You may want to experiment with adding one or both dividers. My pictures below are with both dividers inserted.
Stack your cigars inside the KRUS, being careful to leave room for your humidifying element.
Insert your humidifying element and hygrometer into the jar
Seal the top with the clasps
Remember that this is not a wooden humidor, so you will have to open it from time to time to let some air circulate through it.
Optional step is to add a thin layer of caulk or something to the lid to improve the seal, but I have not found this necessary.
This image shows a full KRUS with about 45 cigars and a small jar of gel solution.
This image shows KRUS filled with about 22 cigars and I left the middle section open for a standard sponge filled with solution suspended in Tupperware. This maintained 72% relative humidity.
All in all, this is am amazing humidor solution for about €6. They also sell smaller versions that you can use to travel or keep in your golf locker, work cabinet, etc.