What you are seeing is the foam lining on the inside/outside door. It is used to completely seal off the outside air when the A/C control is in Recirc mode.
Your filter, if you have one, will be in the inlet vent that is to right of stairwell as you enter the coach. When in Recirc mode, air will be drawn from within the coach, through this vent, and run through the A/C evaporator and on to the dash outlets.
2008 Monaco Camelot 40' PDQ