Good route from Fulton, MS to Hilton Head, SC?

[yumadons]

We did the first half of the TransAm from the OR coast to Pueblo, CO, this year and have 2 months to do the second half starting 9/1/12. We'll take the TransAm from Pueblo and want to adjust the route to end at Hilton Head, SC. My thought is to take the TransAm to the Underground RR south to Fulton, MS, then cut across AL & GA to Hilton Head. Would appreciate any suggestions on getting from the Underground RR to Hilton Head. We're slow, 40-50 miles daily unless tailwind.

Suzanne
Yuma, AZ