Dan McCarthy has serious doubts about Santorum's appeal in the South: 

If Santorum can survive New Hampshire, the Palmetto State will finish him off. The media, rather than look at the actual record of the S.C. primary, continues to see the word "South" and think of religious-right voters. But South Carolina went for Dole over Buchanan in ’96 and McCain over Huckabee in ’04. It’s the state that put Lindsey Graham in the Senate, after all, and if I’m not mistaken it’s the state with the highest number of political consultants per capita in the country. It has an unusual, highly establishmentarian political culture.

Romney's South Carolina strategy:

Romney’s hope for South Carolina is that Gingrich, Santorum, Congressman Ron Paul and Texas Governor Rick Perry will split the conservative vote sufficiently to allow a low showing—perhaps even less than the 25% he won in Iowa—to give him a win.