I just did this install- the directions are great. I recommend pulling the glove box door off to get to the lower screws.
I think the STP1766 filter is just about a perfect fit. As the DIY states, be sure the air flow arrow is down.
You'll see when you slide it in that there are plastic rails in the back that "lift" it up off the bottom of the enclosure. The filter seems like it's meant to have those rails on the "door" lift it up in the front also.
When you open the filter enclosure, just take off the door, slide the filter in, and close it making sure that the filter sits up on top of the rails.
Happy filtering.
Takes ten minutes.