There will be cars on the show field Saturday, judging is on Friday, Sunday morning it's over. They always take too long to come up with an itinerary which does add to the confusion. Take a lot of cash if you want to eat or do anything, the Mondello lectures are free.
http://www.alleghenyrockets.org/nationals.htm
Google Earth the place and look at the layout.
The hotel and the show field can't be too far apart, the swap my be a short walk.