I have been using this excellent Humidifier (Humistat #1)
made by the Humistat Co. for a year now,
and have found it to work wonderfully:
http://www.humistat.com/Humistat_Model-1.htm
If you don't have a way to add some moisture
to your concertina this winter, this is an nice
investment. It does not leak. Made in USA.
Inexpensive. Fits nicely in the case. And it works!!