This is a wall vent built to support 120mm fans. I designed this to move hot air out of my networking closet, I used a 5v Noctua fan and 6x1 1/4th drywall screws. 

The pieces simply slide together; I used caulk to seal the pieces, but this isn't required. The vent side has a hole so you can have the fan cable come out that side. I also used a 2 pin fan connector to USB and plugged it into a UPS for power, if you go this route, MAKE SURE YOU BUY A 5V FAN, 12V fans will NOT work well with the USB.