I've tried shooting the last few car shows and I can only tell you the conditions and not some definite settings.
Lighting will be relatively dim for the camera. In order to get nice DOF for the car, you will want to close up the aperture, but this will lower your shutter speed even more. Bumping the ISO up is 1 solution and using flash is tricky becos it may reflect of the car to give you 1 fantastic hot spot.
There's a mix of flouro tubes and incad spot lights for lightings all over so WB is also another tricky subject. Bring a monopod will be good. There wun be space for tripod set up (though I've seen ppl using it). Since you have an IS lens, make this is the time to make full use of it. 28-135 is quite suitable for this occasion.
With a 50mm after the crop factor, you wun be able to move out far enough without people blocking you, unless you go during weekdays (today is the only weekday left) and in the mornings ( which is now..) where there is very little people.
It's a good training ground.