I am looking into a similar system, if you go to any of the professional gardening suppliers they sell an even better system that controls the humidity with a very fine mist, I will post the address when I find it.
At the moment I use a baby's humidifier that I bought on ebay these are ideal for small scale production as they control the heat also.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 67401&rd=1
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Franco