We stayed at a KOA in SOUTH Carolina....maybe 8 miles from the border...and not too far from the "Hall of Fame" or various driver garages (headquarters). IMO, your problem would not be getting TO Charlotte...but the various garages are really far apart....one end of the city to the other. But...the Hall of Fame will give you the address, etc....and good luck finding them. For instance, for just one day, we went to the Hall of Fame then to Michael Waltrip Racing...and that did the whole 10 hour day. Hope you're there for a few days to really enjoy things..
G'luck and enjoy! Oh..and, BTW, we found that KOA to be just fine...even tho the entrance is a little strange (a fast food place).