I've lived here in Charleston all my life. It is easily doable to negotiate 17 through Charleston, but if you do get in the wrong lane you will be in trouble before you know it. For that reason, if you haven't been through 17, I strongly recommend catching 526 to bypass all of the traffic and lights.
You will save time and fuel by taking 526 not mention the headaches.
As you come into Charleston, stay in the right hand lane to catch 526. After crossing the second tall bridge, take the 17N exit toward Georgetown. The KOA will be a few miles up on the road.