You should decide which you would like to be located near MB or Charleston. The drive in traffic gets old real quick and doubtful you can get to Charleston in 90 minutes. There is a fairly nice KOA on highway 17 as you come into Charleston from MB, there is a camp ground at Givans State park but it is a lot longer drive to downtown. The Oak Plantation is well located for many of the places you might want to go. If you want just a place to stay you could check out the Exchange Club/Fair Ground in Ladson it is just a jump onto I-26 and a twenty minute ride to down town. You may be the only one there depending on when you come in but they have electric and sewer, no pool or anything like that.
If you think you might want to go to Savannah then stay in Charleston for sure we are two hours away a little less if you stay at the Oaks. Not sure what you might need but I live here and would do anything I could to help you.