Venting room-in-room wall

[RFw3Duwrd7Yu]

In order to address damp walls (partially underground) in our kitchen at the back of the house, I've built a wall-in-wall using a steel track & stud system. This has done wonders for dampness in the room, however I'm now to the stage of closing up the various openings, particularly re-instating the window reveal which will seal off the air gap (which is about 150mm) behind the new wall. The room has an always on axial fan running, and I'm keen to avoid doing another core through the wall and carrying out more of the heat in th room, but this fan doesn't technically take air out of the gap between new wall and original wall. I'm thinking it would be good to add some venting, perhaps along the sides of the window reveal, and perhaps also at the top in a few places. Or would it be better to install a small quiet fan to pull air out of that void and circulate it? Any specific kit people would recommend?

 

[foxhole]

Can you explain those terms? Room in room, wall in wall?