First car show -- advice??

That's definitely a concern. Nobody wants some careless twit to walk by and scratch their car -- trailer queen or rust bucket.
I had someone leaning against my freshly painted car once. I had stepped away from it for a few minutes and came back to find some dickhead leaning on it like it was his. He was very lucky that I didn't take his f'n head off, but I did rip him a new one.