A 3" hole will need to be cut in the wall where you wish to place the vent at (be sure not to put this where a stud is at) this is where the round part goes into - it will be on the inside of your trailer.
The 1/2 moon goes on the outside of your trailer matching up to the round part so the flat side of the 1/2 moon faces your trailer. These can be screwed or riveted on. Typically one vent is placed at the top on the front of your trailer and the other at the bottom on the back of your trailer.
