What are these panels underneath the wing root of a A380?
They are indeed the Ram Air Outlet Doors.


(source, showing Ram Air Inlet (RAI) and Ram Air Outlets (RAO))

From the A380 FCOM (21 - Air Conditioning):


  PACK DESCRIPTION
  The hot bleed air flows into each pack, via the two pack valves, then enters the heat exchanger. This
  heat exchanger precools the air using external air. This external air enters through a ram air inlet door,
  and is then discharged overboard through two ram air outlet doors.




The reason they are located in the wing root is that the entire packs are in the wings. From this article:


  The A380's wings are big enough that they can hold the plane's air conditioning packs. That, says Airbus, is an advantage over most other large planes because the packs don't have to be stored in the A380's belly fairing. That, in turn, means the plane's fuselage is more streamlined than it would otherwise be, reducing its drag.