I've stayed at the Mt. Pleasant KOA a couple of times. Its off of US 17 about 8 miles northeast of the bridge. Nice roomy sites and far enough off of busy US 17 to avoid road noise. Next to a huge lake. The entrance road is on the left about 8 miles from the bridge. FHUs including cable and WIFI.
BTW, if you miss it and drive your 'C' with a toad attached over the bridge into downtown Charleston during rush hour, you won't enjoy it. Don't ask how I know.
If you're interested, visit Patriot's Point in Charleston. Home of the WWII Aircraft Carrier Saratoga. Its a museum now. Not many of them left.