Humidifiers and Dehumidifiers - Help installing Honeywell HE360 Humidifier

I purchased the Honeywell HE360A. I don't think I have enough duct space to install the unit. My first thought was the unit could be installed on the oposite side of the top section of silver duct, oposite the vent pipe. (See Images) The problem is, it is too narrow. The only other option I see is on the right side just below the white PVC AC drain pipe. I'm concerned this space might have mechanical parts on the other side. It is also on the return side of the unit and is much thicker metal than standard duct. From what I read in the instructions, they want it to be installed on the other side of the AC coils. I'm not sure where to go from here. Should I purchase a smaller unit?

My house is 3400sq feet. The unit is Janitrol/Goodman CAPF030A2A gas furnace.
http://i455.photobucket.com/albums/qq274/dwightmorrisva/100_7215.jpg

Any help is greatly appreciated!

This furnace is in the attic, and I would not advise of putting the humidifier on this.

You are at risk of water freezing if if freeze up there in the winter months.

This is good to know. Thanks for the warning. That makes sense. It could freeze in the coldest months.

The first floor unit is an all in one self contained package unit that sits outside. We are on a crawl space. The duct work just inside the house is hidden under a staircase that is dry walled in. No access to a close by drain or water supply.

What are my options?

Thanks again for your help!

What are my options?
I am afraid it's going to be the stand alone unit in your home.

Thanks again for your help!
You're welcome!

Ok, that's what I thought you might say.

I appreciate your help.. the stand alone unit it is!