Mount Holley area campgrounds?

Not sure where in the Mt Holly area you'll be but you're right, not much around there. Looking at the list from RV Park Reviews, some of those parks are not very desirable locations and on the east side of Charlotte - Mt Holly is on the west side. We have stayed at Lake Norman MotorCoach "Resort" several times but they are now too expensive for my preference. You can also check out the campground at Charlotte Motor Speedway. While it's on the east side of Charlotte, it is close to I485 which will get you over to Hwy 27 and to Mt Holly area. There are several other CGs close to both those that I don't have personal experience with but have ok reviews. There's a cluster of them right around the speedway and this years NASCAR race is over so shouldn't be a problem getting in one of them. Not sure how long you are planning to stay but maybe try one of the higher rated ones for a few nights and check out some of the others to see if you want to move. Some may recommend the CG at Carowinds or Ebenezer Park in Rock Hill SC but with traffic and the only access to the north is I77 and I don't think you'll want to deal with that.

Hope this helps.