Fly trap

Problem is you get one in, it lays eggs and now you have 12. A couple of them survive to mate, and the cycle continues with the flys becoming smaller and smaller as inbreeding and a lack of food take their toll. 5 days later the truck is fly free, and then you pick up a new fly and you start all over again.

 

Make a loop, sticky side out, of the fly paper and stick it to a spot on the dash or glass or ceiling. Won't duct tape work just as well as fly paper? I'm a tinkerer. Some people want a purpose-made device for every single different function in life. It's OK to be creative.

Plastic bottle will also work.
https://www.youtube.com/shorts/x8zHcRsnhao

 

If both ends of the fly paper are stuck to something like a cabinet, windshield, or side window nothing is swinging in the wind or moving around like a pendulum.

If you don't want the flypaper goo on something, put a piece of duct tape under the place you stick the flypaper.

Cut the top cone-like section off a plastic bottle. Turn in so the mouth is now inside and pointing down into the bottle. Leave a bit of sweet soda in the botttle. The fly fly or walk into the bottle but they can't fly out.

 

Fly’s sleep at night and will always search for a safe place to go. Sunset is the worst time for flys getting in your truck.

They also hate the cold so if you got one buzzing around your head just crank the AC and they’ll calm down.

They are quite easy to kill if you got the skilz.
Just clap your hands about 8 inches above where they landed and you’ll get them every time.

Lol, or just use your fire extinguisher.

 

I retired early after driving for 28 years. Maybe I'm doing it wrong.

 

I go to dairies and try as I might, one always gets in. I'm gonna drive off a mountain someday swatting at one.