Warning, this subject is old (1621 days without answer)
Baube
Often... still doing it from time to time .
I also write from time to time and one of my characters ended up being a car collector because i just couldn't choose which car he would be driving ....
caravan
When I was younger I used to daydream a lot about making up TV shows or movies and what the characters would drive. I still do it sometimes. But I would take elements of real TV shows or movies and mix them with things that have happened to me in real life along with real vehicles, places etc. It was kind of fun, but I never had the imagination to make up a whole story line. It was mostly just specific scenes with the vehicles involved.
I bet others of us have too, since this is the IMCDb after all.