Made it up myself, although I'm sure its been played before.
Wife and I just got back from traveling from CA to WI/IL and back. We were towing a car trailer (not our Airstream this time)...and on the return trip sans trailer.
From the first mile we played the game. Who can spot an Airstream first and yell it out.
After 17 days there and back I won with a count of 34 to 32.
We also put in a minus count of one if you yelled "Airstream" and it turned out NOT to be one. I was penalized 4 times.
It made for a interesting drive not only checking the road but a lot of back yards and lots.
Maybe you played it before but using VW Bugs...when you traveled with your parents...back in the day.