Willi, don't play around with that cooler or container stuff. Just use a plastic tube about 2 meters long, seal it on one end with gaffers tape and work in a piece of cord about 1meter long. The cord is for free hanging in the bow in the tube. hang the whole setup at the ceiling, the other end of the tube should reach the floor. Put the pot with the ammonia in this end of the tube and seal with some rubber band.
That's all!
You can watch the tranformation through the transparent plastic esily. I usually go for one day ub to seven days. When putting out the bow let the damp vaporize out (go out for that - it stinks heavily).
Good luck!