Anybody help with the filter on this HVAC system?

Just inspected a trailer home today. In the wall of the laundry room is this furnace. The top panel on the furnace is louvered and acts as the return. Directly behind this louvered panel are the A-coils. I see no way to add a filter on this system behind this panel. Currently it appears that the only thing filtering any of the air are 2 metal filters that look like grease filters. From the photos below can anyone tell me how the filter for this system SHOULD be installed…Surely these metal grease type filters are incorrect.

As much apperant rust that is present, I would be more inclined to report near end of life, have qulified heating/air contractor to inspect it.

That’s how they come

I usually see the filter mounted on the door where the air return louvers are located. Usually a spring steel wire that hold the filter flush on the inside of the door. Mark

I am sure this site should help you out.

Get that grease filter out of there!

You’re going to end up with water damage.