The GSMNP is a rather large area. You really need to narrow it down a bit. These sites should help you to narrow your choices down a bit. One is a commercial site and the other is the offical GSMNP site. It would take you several visits to really "see" it all. Don't for get to take a jacket with you. It gets a bit cool at night, especially when it rains (I think we may have a wet summer this year). W've been sleeping under a light blanket at night and we are only at 3200ft... far lower than most of the park.
http://www.gsmnp.com/
http://www.nps.gov/grsm/ (BTW, for the NP campgrounds, we have found that the "max RV size" usually means that that is the biggest RV that will fit on the smallest site in the campground)