My dad has the same problem with his car. No matter what it's there and is too quick for him to be rid of it It's an ideal place for the spider, dark, easy to access and a permanent home. A car is stationary for many hours so the spider can be undisturbed and they always seem to be nocturnal, well I see many more moving about if I'm up late, and come back to it easily. Spiders are peculiar and ugly things.