Whole house humidifier placement

I moved into a new house and was looking to add a whole house humidifier and upon inspecting the furnace there was a patch where it looked like they placed one before. I removed the patch and filled the airconditioner coil so it appears they added it after the fact. There is no room anywhere else to place. My question is can I place below the coil and just above the furnace? Here is my picture. Using a Aprilair 500.Attachment 42801 (http://www.doityourself.com/forum/attachments/humidifiers-dehumidifiers/42801-whole-house-humidifier-placement-image.jpg)