Here are some pictures of the installation: http://imgur.com/a/UWSyD
This furnace is actually in my unit. It looks like the previous tenant or landlord just jammed a bunch of filters on both sides. I find it hard to believe that this is the right installation but can't really figure out how a filter should be properly installed? Has anyone seen anything like this? Or was the whole furnace just not installed right to begin with. Seems very weird. The 4th and 5th pictures are what is on the opposite side of the furnace.