You will be able to leave trailers overnight but will not be able to stay in the motorhomes at the race track site (Disney ESPN Wild World of Sports). As many have posted on here the Animal Kingdom campground at Disney are where several people will be camping with their motorhomes.
The racetrack will be on the premise of the ESPN Wild World of Sports...
http://disneyworld.disney.go.com/destinations/wide-world-of-sports/As you can see from the pic its a pretty impressive complex.
Joe feel free to email or call me if you have any other questions. We are looking forward to the event!