Well I'll be! I do have filters! Four in the Sanibel and they were dirty.
I didn't bother with replacing the staples. The cardboard and the vent frame clamp the foam in there pretty good (plus the two screws going thru on the end).
What irked me was this. There was a whole lotta sawdust on one (long) edge of the holes from where they'd cut out the plywood ceiling for the vent. I vacuumed it out. Guess where the sawdust is from the other long edge? I don't know for sure, but I'll wager that it was sucked into the evaporator coils the first time the AC was turned on. Why do you worry about putting in filters if you're going to clog everything up with sawdust!!!