sink drain screen
I did something similar with using a stainless steel sink drain screen. I made a bug screen for the fresh air inlet. I marked a 3" diameter circle with a Sharpie on a 4.5" diameter mesh strainer (Home Depot, Danco part # 88822). I then trimmed around the perimeter of the strainer, next to the outer band. The line I marked was the "bend" line for the screen. I bent it in three "stages" to get and nice, clean bend. I then inserted the mesh into the 2" tubing and proceeded to bend it back around the outside of the tubing. This made a nice dome shaped screen on the inside of the tube. I taped the screen in place with some electrical tape and then slid it over the NACA inlet and used a hose clamp to hold everything in place. This should work out fine. I can always remove it if I want.
I hope this helps.
Jeff