I 95 is shut down between 20 & 26, due to flooding. Also, parts of 77 are underwater - if your route takes you into the state, check the conditions before you go.
Truckers are a determined bunch. When a major corridor like I-95 is closed down, many will seek alternate routes, taking their heavy loads onto secondary roads where the ground is absolutely saturated. The rain is forecast to stop this morning. Hopefully I-95 will reopen soon.
301 is the reported alternate route. Been in Myrtle Beach from the beginning of this stuff. It is a mess. Florence (I95) and Darlington (I20) County had a mandatory curfew last night. Expired at sun up this morning.
After what I read today, I'd stay out of SC altogether for the time being. Over 500 road closures, numerous flooded roads, and the promise of more to come, as rivers continue to top flood stage, and will for probably another week yet.