Tim,
They were a permanent adhesive (not top quality) but, some people used them as one-time use. Usually go right on the paint or onto the pre-painted number area. I think the dirt bike racer use similar numbers, they usually come as a approx 12" x 6x" or similar.
I would have loved to drive with you guys at the 4 hour Kart enduro.
My vacation timming wasn't the best, I also missed the autox, plus I wanted to see the tecate for the first time.
But I had a great time in the rainy Switzerland and finally got my helmet custom painted by my dad so I won't look like an astronaut with a white helmet he said
We also took his F3000 Reynard/Judd apart after the race with the InterSeries in Most (CZ) to setup the car for the next race. These cars are just built to race and so easy to work on.