Suggestions for Windshield mounted gps lap counter / timer ?

I have three cars i want to take to the track this year would like a device i can move between them.

Dean

 

I don't believe any group will let you run with a temporarily mounted object in your interior since in an accident it will become a projectile...perhaps you can tape it in the rear license plate area like most track timers are placed or on your rollbar like a camera mount...but no way on the windshield