Humidifiers and Dehumidifiers - Virtually No Return Plenum

Hello, and I would like some advice please. I want to install a whole house humidifier, and from my reading of your posts, most of you prefer the bypass types vs. fan type. My problem is that I have a 1700sf condo and the Bryant upflow furnace is located in a utility closet with the return air fed from the opposite side of an interior wall with only 2" between the furnace and inside the utility closet wall, therefore virtually no return plenum to use for bypass hookup. Also, the supply duct is insulated ductboard but I can mount some hangers or install enough solid sheet metal to mount unit on supply side.
Should I go with a powered fan or drum unit then? Or do you have any other suggestions? (I'm sick of the portables)
Thanks in advance,
---Frz

If you don't have return ductwork, then you will have to use the fan powered unit on your supply side of the ductwork above the A/C coil.