It's pretty easy to solder a brass tube in the vent hole. I've done it several times. Put a piece of fuel tubing on the tube and run it inside the airframe. That diaphragm only leaks when it's broken. I ran the fuel tubing from my vent to a little plastic pill bottle with a cap on it and a hole in the top. If the diaphragm wears out, it won't leak fuel inside my plane. I mounted the pill bottle where it is visible for inspections.

I've seen guys simply cut up a Coke can and punch a few holes in it to match the vent plate screws. Remove the screws from the vent cover and put your "air dam" on top of the plate. Run the screws back in. It deflects incoming air from passing directly over the vent hole.