I can't believe you started this thread. Yes, I'm one of the geeks in the crowd. I used to have an ASI
and altimeter out of an old Stinson in my '75 Chevy Impala. I had a 1.5 foot pitot tube painted red and white sticking out the front with a quick disconnect for when I parked it nose-in to a sidewalk. I experimented with the location of the tube to get the most consistent reading. After running it for a while with the A/C on normal and recirculate I realized I needed a static system too, so (like a geek) I also ran a static tube. The best place I could find to terminate it was in the trunk, but I still think I could have done it better with more experimentation (this all happened 20 years ago).
It was an entertaining project and I learned a lot about aerodynamics from it, like wake turbulence behind a truck and how far back it extends at various speeds.
The altimeter was not quite as much fun since I was using it around the substantially flat terrain of West Texas. The variation of barometric pressure made a bigger difference than the terrain change.