Here is a step by step instruction that works. If this does not work for you then contact a GM and tell him your game is glitched because I just tested it.
#1 Make A large or small wooden crate (A square one is prefered due to the rectangle boxes having a tendency to occasionally bug up) with a carpenter, it must be lockable, so high carpentry skill is needed.
#2 Make your trap (Tinker skill), the Dart Trap is the best and easiest, but it takes a little fletching skill to make the Crossbow Bolt. The lower you tinker skill the better for this part (30 is ideal as it is the lowest you could do it) get a a talisman with tinker success chance bonus to help with success to trap the box.
#3 Lock the box with the key and place it on the floor of your house and secure it.
#4 Use a decoration tool and turn the box one time. (the box must face with its long axis east-west otherwise the trap does not work)
#5 Unsecure the box and cast magic unlock (do not use the key to unlock it, that removes the trap), you then should have a trap box that will always stay trapped for you with low damage output.