Regarding travelling through South Carolina. You can legally transport your loaded firearm in your vehicle in South Carolina w/o a carry permit as long as it is secured in a glove box, console, etc. You just cannot have it on your person. Definitely look up the SC statutes to verify for yourself.
Here is the relevant section of the S.C. annotated code on the transport/carry of firearms.
SECTION 16-23-20. Unlawful carrying of handgun; exceptions.
It is unlawful for anyone to carry about the person any handgun, whether concealed or not, except as follows, unless otherwise specifically prohibited by law:
(1) regular, salaried law enforcement officers, and reserve police officers of a state agency, municipality, or county of the State, uncompensated Governor's constables, law enforcement officers of the federal government or other states when they are carrying out official duties while in this State, deputy enforcement officers of the Natural Resources Enforcement Division of the Department of Natural Resources, and retired commissioned law enforcement officers employed as private detectives or private investigators;
(2) members of the Armed Forces of the United States, the National Guard, organized reserves, or the State Militia when on duty;
(3) members, or their invited guests, of organizations authorized by law to purchase or receive firearms from the United States or this State or regularly enrolled members, or their invited guests, of clubs organized for the purpose of target shooting or collecting modern and antique firearms while these members, or their invited guests, are at or going to or from their places of target practice or their shows and exhibits;
(4) licensed hunters or fishermen who are engaged in hunting or fishing or going to or from their places of hunting or fishing while in a vehicle or on foot;
(5) a person regularly engaged in the business of manufacturing, repairing, repossessing, or dealing in firearms, or the agent or representative of this person, while possessing, using, or carrying a handgun in the usual or ordinary course of the business;
(6) guards authorized by law to possess handguns and engaged in protection of property of the United States or any agency of the United States;
(7) members of authorized military or civil organizations while parading or when going to and from the places of meeting of their respective organizations;
(8) a person in his home or upon his real property or a person who has the permission of the owner or the person in legal possession or the person in legal control of the home or real property;
(9) a person in a vehicle if the handgun is:
(a) secured in a closed glove compartment, closed console, closed trunk, or in a closed container secured by an integral fastener and transported in the luggage compartment of the vehicle; however, this item is not violated if the glove compartment, console, or trunk is opened in the presence of a law enforcement officer for the sole purpose of retrieving a driver's license, registration, or proof of insurance. If the person has been issued a concealed weapon permit pursuant to Article 4, Chapter 31, Title 23, then the person also may secure his weapon under a seat in a vehicle, or in any open or closed storage compartment within the vehicle's passenger compartment; or
(b) concealed on or about his person, and he has a valid concealed weapons permit pursuant to the provisions of Article 4, Chapter 31, Title 23;
(10) a person carrying a handgun unloaded and in a secure wrapper from the place of purchase to his home or fixed place of business or while in the process of changing or moving one's residence or changing or moving one's fixed place of business;