that looks nice and clean fdd,
i just sheetrocked the opening to my secrect closet and sealed the whole thing off and painted it to look like the rest of the wall. now I have a 20"x20" vent that is the only acess to the secret garden, wish i could post pics but would ruin the secrecy of it but im tellin you there nothin like haveing a secret passage in you secret spot, plus it can double as a panic room.
for light proofing the vent without cloging it i pinned a light proof curtain flap with it just hanging on the bottom. still have a lil light leak which reveals the secret still gotta work on that part